Comparison of laser cladding properties of tantalum and tantalum pentoxide powders on titanium substrates

doi:10.21203/rs.3.rs-3766135/v1

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Comparison of laser cladding properties of tantalum and tantalum pentoxide powders on titanium substrates

https://doi.org/10.21203/rs.3.rs-3766135/v1

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published 01 May, 2024

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Tantalum (Ta) has excellent mechanical properties, biocompatibility, and corrosion resistance. However, its application is limited by its high cost. Tantalum pentoxide (Ta₂O₅), a stable oxide of Ta, is a key role of Ta surface with excellent biological properties and corrosion resistance and has the advantage of a lower cost. In this study, Ta and Ta₂O₅ powders were preplaced on titanium (Ti) substrates and irradiated by a diode laser to form single-layer single-pass coatings. For comparison purposes, the scanning process was performed using a range of laser powers (1000, 1500, and 2000 W) and scanning speeds (3–5, 4.5–7.5, and 6–10 mm/s). The Ta coatings showed no surface cracking. However, spherical pores were observed near the fusion line of the coating with the substrate in some samples. The porosity increases with the decrease of laser powers and the scanning speeds. The formation of these pores was attributed mainly to the evaporation of the Ti substrate during the cladding process and the subsequent entrapment of the vapor bubbles within the coating. The Ta₂O₅ coatings showed almost no pores but exhibited few transverse cracks on the coating surface as a result of the thermal expansion coefficient mismatch between the ceramic coating and metallic substrate. For all of the coatings, the coating hardness was significantly higher than that of the substrate. The Ta₂O₅ coatings (580–700 HV) showed a higher hardness than the Ta coatings (350–400 HV). Moreover, the coating hardness remained approximately constant through the coating depth, whereas that of the Ta coatings showed a notable reduction with an increasing distance from the coating surface.

laser cladding

Ta2O5

pore

crack

Titanium (Ti) and its alloys have many favorable properties, including high specific strength, relatively low elasticity, excellent biocompatibility, and good corrosion resistance. Consequently, they have been widely used as implant materials for dental and orthopedic applications [1–4]. However, Ti and its alloys are bioinert, and hence hard fibrous tissue is formed around the implant due to poor osseointegration. The resulting stress shielding effect leads to bone weakening and shortens the life of the implant [1]. Therefore, the bioactive surfaces of biomedical implants are generally modified by coating with a suitable material [5–7] and/or modifying the surface properties via appropriate techniques [5, 8].

Two of the most commonly used materials for the surface treatment of metal implants are hydroxyapatite (HA) and fluorapatite (FA) [6, 9–11]. Both materials have a chemistry and structure similar to those of bone and tooth minerals and thus exhibit excellent biocompatibility and bioactivity [8]. However, they have poor mechanical properties, resulting in a limited service life.

Tantalum (Ta) and Ti have excellent mechanical properties. Of the two materials, Ta has superior biological properties and corrosion resistance in harsh environments [12–19]. Therefore, it has received significant attention as a bioimplant material in recent decades. However, Ta has a very high density and extremely high melting point (3017°C), making it difficult to produce modular all-Ta implants using traditional processing methods [13]. In addition, Ta is a rare metal with limited reserves and a high cost, which greatly limits its application [13], but Ta is more suitable as a candidate coating material in biomedical applications. The enhanced corrosion resistance, wear resistance, and biocompatibility of Ta implants arise mainly as a result of the ability to grow a dense Ta₂O₅ passivation film on the surface, which has high stability over a wide potential-pH range [20–24]. Thus, Ta₂O₅ has long been considered an excellent biomaterial. In addition, the melting point of Ta₂O₅ (1882°C) is lower than that of Ta, making Ta₂O₅ easier and cheaper to process. Consequently, the application of Ta and Ta₂O₅ for medical implant coatings has received great interest in recent years [14, 17, 19, 23, 25].

Various processes are available for the fabrication of Ta or Ta₂O₅ coatings, including plasma immersion ion implantation (PIII), sol-gel, chemical vapor deposition (CVD), and physical vapor deposition (PVD) [17, 21, 26, 27]. However, because of their slow growth rate, the thickness of the films fabricated using these techniques is typically less than 100 nm. Therefore, laser cladding, which offers a high deposition rate and adjustable coating thickness, is often considered to be a more advantageous method [5, 28].

Laser beam irradiation provides an intense source of high-coherence electromagnetic radiation and can produce a strong metallurgical bonded substrate-coating interface when used for cladding [5, 29, 30]. Among high-power lasers, compared with CO₂ or Nd:YAG lasers, diode lasers have high energy efficiency, a long lifetime, good absorptivity in metals, and low capital and operating costs [31, 32]. Furthermore, laser cladding is a layer-by-layer near-net-shape process capable of producing three-dimensional complex parts [33]. Therefore, diode lasers are widely used for the fabrication of surface coatings on implant materials [31–33].

Many studies have examined the use of Ta or Ta₂O₅ as bioactive coatings for metal implants [17, 19, 25, 28–30]. However, Ta is a metal, whereas Ta₂O₅ is a ceramic, and the metallurgical properties of laser-clad coatings vary significantly depending on the coating material. To the best of the authors’ knowledge, the laser cladding performance of Ta and Ta₂O₅ coatings has not yet been compared in the literature. Thus, the present study pre-places Ta and Ta₂O₅ powders on pure Ti substrates and then uses a diode laser to prepare single-layer single-pass clad coatings at different laser powers and scanning speeds. The effects of the laser process parameters on the microstructures and hardness of the various coatings are then evaluated and compared.

2.1 Cladding powder preparation

Ta powder with a purity > 99.9% was purchased from G-Smelt Precious Metal Co., Ltd. (China) with a particle size distribution of 5–50 µm (see Fig. 1(a)). The particles mainly showed an irregular spherical-like shape, although a small number of them had an elongated appearance due to agglomeration. Ta₂O₅ powder (see Fig. 1(b)) was obtained from the Ta powder via a one-step thermal oxidation process in which the Ta powder was heated to 900°C at a heating rate of 5°C/min and held for 30 min [34]. The Ta₂O₅ particles were noticeably smaller than the Ta particles, with sizes ranging from 2 to 20 µm.

2.2 Sample preparation

Commercially pure rolled titanium (CP-Ti) plate (100 × 60 × 3 mm³) was used as the substrate material. Grooves with a size of 50 × 3 × 0.5 mm³ were machined on the substrate surface (see Fig. 2) to allow the thickness and width of the pre-placed powder layers to be precisely controlled. The Ta and Ta₂O₅ powders were placed in the grooves, and the substrates were then immersed in ethanol, and ultrasonically agitated to ensure a uniform thickness of the pre-placed layers. The substrates were then removed from the bath and air-dried.

2.3 Experimental cladding process

A high-power diode laser (LDF 4000-60, Laserline, Germany) with a maximum power of 4.4 kW and a wavelength range of 978–1025 ± 10 nm was used to fabricate the Ta and Ta₂O₅ coatings. The laser working distance was set to 138 mm, and the beam size was set as 4 × 4 mm². The experiments were conducted in an argon (Ar) protective atmosphere using a self-made mask, as shown in Fig. 3. The Ar flow rate was maintained at 25 L/min, and cladding was performed using a robotic arm (ABB Robot (Irb 6700)) with a movement radius of 2.5 m and positioning accuracy of 1 mm.

To simplify the processing experiments, the laser beam size and shielding gas flow rate were kept constant, while the laser power and scanning speed were varied, as shown in Table 1. Table 2 shows the thermal properties of the Ti substrate and Ta and Ta₂O₅ powders [13, 35, 36]. It is noted that the melting point of Ta is significantly higher than that of either Ta₂O₅ or Ti (1668°C). Thus, the experiments provide useful insights into the impact of the difference in the melting point between the coating and substrate material on the melting and solidification characteristics of the laser-clad coatings. As shown in Table 1, the cladding experiments were performed using three laser powers: 1000, 1500, and 2000 W. To obtain a similar specific energy across the considered power range, the scanning process was conducted at three carefully chosen velocities in the range of 3–5 mm/s, 4.5–7.5 mm/s, and 6–10 mm/s for laser powers of 1000, 1500, and 2000 W, respectively. The specific energy was calculated as E_s=P/(D×V), where P is the laser power, D is the laser beam size, and V is the laser scanning speed [5]. The resulting specific energies for each laser power were approximately 83.3, 62.5, and 50 J/mm², respectively.

Table 1

Variable and constant laser cladding parameters.
Laser parameters
Variable parameters				Constant parameters
Specific energy (J/mm²)	Laser power (W)	Scanning speed (mm/s)			Beam size (mm x mm)	Focal length (mm)	Shielding gas flow rate (Ar, L/min)
83.3	1000	3, 4, 5	4 x 4			138	25
62.5	1500	4.5, 6, 7.5
50	2000	6, 8, 10

Table 2

Thermal properties of Ti substrate and coating materials.
	Ti	Ta	Ta₂O₅
Melting point (°C)	1667	3017	1882
Boiling point (°C)	3287	5425	n.a
Thermal conductivity (W/m༎K)	21.9	57.5	0.3 ~ 0.6
Thermal expansion coefficient (10^− 6 K^− 1)	9.41 ~ 10.03	6.4	4.7
Modulus of elasticity (E, GPa)	120.2	185.7	108

2.4 Morphology, chemical composition, and microhardness

The morphologies and microstructures of the laser-clad coatings were examined using a scanning electron microscope (SEM, Hitachi S-3000N, Tokyo, Japan) equipped with an energy-dispersive X-ray spectroscope (EDS). Phase analyses were performed using an X-ray diffraction machine (XRD, Bruker D2 Phaser, Germany) with Cu Kα radiation (λ = 0.154 nm), a 2θ range of 20–60^o, and a scanning rate of 4^o min^− 1. EDS line scans and mapping analyses were performed to identify the element distributions along the cross-sections of the coatings and to evaluate the dilution between the coatings and the substrate. The mechanical properties of the samples were quantified by microhardness measurements along the depth direction of coatings from the coating layer (under surface 50 µm), interface to substrate using a Vickers microhardness tester (Mitutoyo HM-1300, Japan) with an applied load of 300 g and a load-dwell time of 5 s.

3.1 EDS and XRD analyses of Ta and Ta₂O₅ raw powders

Figure 4 shows the EDS spectra (Figs. 4(a) and (b)) and XRD patterns (Fig. 4(c)) of the raw Ta and Ta₂O₅ powders. The Ta powder consists of α-Ta with a body-centered cubic structure (JCPDS card, No. 04-0788), while the β-Ta₂O₅ powder has an orthorhombic crystal structure (JCPDS card, No. 25–0922). Although the Ta powder is composed mainly of Ta, it also contains a small amount of O, most likely originating from the SEM chamber environment or the spontaneous oxidation of the Ta powder [37, 38]. However, the O is present only in very small quantities and thus does not appear in the XRD pattern. An obvious O peak is observed in the EDS spectrum of the Ta₂O₅ powder, and a pronounced Ta₂O₅ diffraction peak is seen in the XRD pattern. The Ta₂O₅ particles were produced by the thermal oxidation of the Ta powder and have a small size since the density of Ta (16.6 g/cm³) is approximately twice that of Ta₂O₅ (8.8 g/cm³). In particular, as Ta completes its phase transformation to polycrystalline Ta₂O₅, its volume expands significantly, causing the material to break owing to internal stress and form smaller particles [34].

3.2 Surface and cross-sectional morphologies of Ta coatings

Figure 5 shows the surface macro morphologies (×30) of the single-layer single-pass cladded-Ta coatings prepared using various laser powers and scanning speeds. For the sample processed at 1000 W, unmolten or partially molten zones appear on both sides of the coating (scan track) for all E_s values. A similar phenomenon is observed for the coatings prepared using E_s values of 62.5 J/mm² (or lower) at a laser power of 1500 W, and an E_s value of 50 J/mm² in the sample prepared at 2000 W. In other words, at lower laser powers and energy intensities (higher scanning speeds), the heat input to the coating decreases, and hence the powder is only partially melted.

Figure 6 presents cross-sectional SEM images of the single-layer cladded-Ta coatings prepared under the various scanning conditions. For all of the coatings, the morphology has a bowl-shaped profile. None of the coating cross-sections contain cracks. However, for all of the samples other than those prepared with a power of 2000 W and scanning speed of 8 or 10 mm/s, the cross-sections contain some spherical pores (bubble porosity) with a size of several tens to hundreds of microns. The pores are mostly located in the fusion zone (coating) close to the substrate. Many factors have been proposed for the formation of bubble porosity during laser cladding. Two of the most commonly proposed causes are the intrusion of shielding gas or ambient gas into the molten pool and the entrapment of metal vapor in the molten pool due to the rapid solidification process [39–41]. In the present study, the melting point of the Ta powder is 3017°C [13], which is very close to the boiling point of the CP-Ti substrate (3278°C). Therefore, when the laser energy is sufficient to melt the Ta powder, it may also vaporize the Ti substrate near the molten pool. Owing to the rapid cooling rate of the laser cladding process, the vaporized Ti metal has insufficient time to float upward and escape to the ambient environment; hence pores are produced close to the interface between the coating and substrate [41].

Overall, the porosity tends to decrease with a decreasing E_s and increasing laser power. Moreover, for a fixed E_s, the porosity decreases with a higher laser power and scanning speed. This finding is reasonable because as the scanning speed increases, the time available for the thermal energy to be transferred from the coating to the substrate is shortened, and consequently, the amount of vaporization of the Ti substrate is reduced. Similarly, for a fixed laser power, a lower E_s (i.e., a higher scanning speed) results in a lower porosity because of the reduction in the heat input and transfer of thermal energy to the substrate. Furthermore, as the scanning speed is increased under a fixed power, the time available for the thermal energy to act on the substrate is reduced, and thus porosity formation is further suppressed.

3.3 Surface and cross-sectional morphologies of Ta₂O₅ coatings

Figure 7 shows the surface macro morphologies (×30) of the single-laser single-pass cladded-Ta₂O₅ coatings prepared using different laser powers and scanning speeds. Similar to the Ta coatings, a lower laser power and/or specific energy results in unmolten or partially molten zones on either side of the scan track. For a laser power of 1500 W and a scanning speed of 6 mm/s, a small number of transverse cracks are observed perpendicular to the axis of the coating, as shown in Fig. 8. Moreover, no cracks are formed at the interface between the coating and Ti substrate (see Fig. 9).

Xu et al. [20] used a double cathode glow discharge technique to prepare β-Ta₂O₅ nanocrystalline coatings on a Ti6Al4V substrate. The coatings showed strong adhesion to the substrate and strong resistance to deformation and cracking under external loads. However, due to the inherent properties of ceramics, including Ta₂O₅, the mechanical properties of the coating are not only affected by the physical and chemical properties of the coating and substrate but also by factors such as the coating method, processing conditions, and coating thickness. The transverse cracks observed in the present Ta₂O₅ coating are the result mainly of the large difference in the thermal expansion coefficients of the Ta₂O₅ coating (4.68 ×10^− 6 K^− 1) and Ti substrate (9.41 ~ 10.03 × 10^− 6 K^− 1) (Table 2), respectively. Owing to this mismatch and the large temperature gradient induced in the cladding process, a longitudinal tensile stress is generated during the rapid cooling stage, which may even cause the coating to fall off [5, 42–45].

Figure 9 presents an SEM cross-sectional image of the Ta₂O₅ coatings prepared under the various scanning conditions. It is observed that the coating and substrate are well fused, and fewer pores (1500 W and 6 mm/s) are produced than in the Ta coating prepared under equivalent conditions. In addition to the welding metallurgical characteristics, the bonding quality between laser-clad coatings and the substrate is also closely related to the difference in the thermal properties (especially the melting point) of the two materials. In the present study, the melting point of Ta₂O₅ (1882℃) is closer to that of the Ti substrate (1667℃) than that of Ta (Table 2). Consequently, the mutual melting effect of the coating and substrate is improved, and hence the bonding quality is enhanced. Moreover, because the difference in the melting points of the coating and substrate is not too large, vaporization of the substrate material is reduced, and therefore the number of pores in the final coating is also reduced.

3.4 Depth and width of coatings

Figure 10 shows the scan track widths and penetration depths of the cladded-Ta and Ta₂O₅ coatings produced at different specific energies. For both coatings, the width gradually increases with an increasing E_s (decreasing scanning speed) and laser power (Figs. 10(a) and (b)). Although a higher E_s produces a greater coating depth, the effect of E_s on the depth is not as significant as that on the width, which may be related to the higher scanning speed range (Figs. 10(c) and (d)). The maximum width and depth of the Ta cladding layer are 5.1 mm and 1.1 mm, respectively, while those of the Ta₂O₅ sample are 6.0 mm and 1.4 mm.

For a fixed E_s, a higher laser power (higher scanning speed) increases the amount of heat energy input into the coating per unit time and thus increases the melting tendency of the coating. Similarly, for a fixed laser power, a higher specific energy (lower scanning speed) also increases the heat input, even though the power acting on the coating remains unchanged because of the longer laser irradiation time. Thus, the coating melting effect is again enhanced, particularly as the coating width increases [41, 46, 47].

For fixed laser-cladding parameters, the width and depth of the Ta₂O₅ coating are greater than those of the Ta coating. As shown in Table 2, the melting point of Ta₂O₅ (1872°C) is much lower than that of Ta (3017°C). Thus, under the same heat energy input, the degree of melting of the Ta₂O₅ powder is higher; hence both the width and the depth of the scanned layer increase.

3.5 EDS composition analysis and line scan results

Figure 11 shows the EDS analysis results for the surface compositions of the cladded-Ta and Ta₂O₅ samples (2000 W, 8 mm/s). The surface compositions of the two cladding layers are similar and both contain Ta, Ti, and O elements. The average Ta, Ti, and O contents of the cladded-Ta sample are approximately 35 wt.%, 59 wt.%, and 5 wt.%, respectively; while those of the cladded-Ta₂O₅ sample are approximately 18 wt.%, 70 wt.%, and 11 wt.%. The results indicate that after laser irradiation, both coatings are diluted by the Ti substrate to a great extent; however, the degree of dilution of the Ta₂O₅ coating is greater than that of the Ta coating.

In order to analyze the pore-forming mechanism of the Ta coating more clearly, the power was set to 1500 W, and the scanning speed steps were expanded to 15 mm/s (low E_s), 10 mm/s (medium E_s), and 5 mm/s (high E_s) to make the pore formation tendency more obvious. Figure 12 presents SEM cross-sectional images and the EDS analysis results for the coatings produced using low, medium, and high specific energies, respectively. For the highest scanning speed (15 mm/s), that is, the lowest E_s, the Ta particles are only partially melted and many small holes appear in the coating. Moreover, several large and irregular strip-shaped pores are formed at the interface between the coating and substrate (Fig. 12(a)). Strip-shaped pores are a common feature of insufficient laser energy in laser-clad coatings [48]. At a medium scanning speed (10 mm/s), that is, at a medium specific energy, E_s, spherical holes appear in the coating (Fig. 12(b)). Most of these pores are located close to the fusion line of the coating with the substrate. Moreover, most of the pores are situated in the darker regions of the SEM image, which correspond to areas with higher Ti content. Consequently, it seems that the formation of the pores is mainly due to the vaporization of the Ti substrate during the cladding process, and the subsequent entrapment of the vapor bubbles in the melt pool as it undergoes solidification [41]. However, when the scanning speed is further reduced, resulting in a higher E_s, the solidification time of the molten pool increases, and the number of pores reduces because the vaporized Ti bubbles have sufficient time to escape from the coating to the ambient environment (Fig. 12(c)). Figure 13 presents a schematic representation of the differences in the melting degree and pore formation caused by different E_s values or scanning speeds of the Ta coating and Ti substrate.

Figures 14 and 15 show the EDS mapping and line scan results for the cross-sections of the Ta and Ta₂O₅ coatings produced under a high E_s (1500 W, 5 mm/s). The element distributions of the two coatings are consistent with the analysis results presented in Fig. 11. Moreover, the EDS analysis results show that the dilution rate of the coating is significantly increased under a higher E_s because of a greater upward diffusion of the Ti substrate element, which results in a smoother (Ta sample) or uniform (Ta₂O₅ sample) distribution of the Ta and Ti elements [41, 48]. The dilution effect of Ti on the Ta₂O₅ coating is particularly obvious because of the greater mutual melting degree of the coating and Ti substrate, as discussed earlier in Section 3.3.

3.6 Microhardness

Figures 16 and 17 show the microhardness profiles of the Ta and Ta₂O₅ samples along the depth direction of the coatings from the surface to the substrate. The Ta coatings have a hardness of around 350–400 HV_0.3, whereas the Ta₂O₅ coatings have a hardness of approximately 550–700 HV_0.3. The hardness of both coatings is thus significantly higher than that of the Ti substrate (160 ~ 180 HV_0.3). For the same processing conditions, the hardness of the Ta₂O₅ coating is much higher than that of the Ta coating. The hardness profile of the cladded-Ta sample reveals an obvious smooth downward trend from the coating surface to the substrate. In contrast, the hardness of the Ta₂O₅ sample remains approximately constant through the coating depth.

For the Ta sample, the hardness distribution reduces smoothly on both sides of the coating-substrate interface. Balla et al. [12] observed a similar phenomenon in laser-cladded porous Ta coatings on Ti substrates. The authors suggested that the smooth change in the Ta coating hardness was due to the absence of undesirable phase formation in the reaction between Ta and Ti. The EDS line scan results obtained in the present study (Fig. 15) show that the Ti diffusion into the Ta coating gradually reduces with an increasing distance from the substrate. However, a similar tendency is not observed in the Ta₂O₅ sample; rather, the Ti content of the coating remains approximately constant. This may explain why the Ta samples show a smooth decrease in hardness toward the substrate, whereas the Ta₂O₅ samples do not.

Many factors affect the hardness of coatings, including Hall-Petch strengthening, dislocation strengthening, and solid-solution strengthening. These strengthening mechanisms are closely related to the coating process and coating materials [49]. For example, laser cladding is a rapid heating and cooling process, and hence the coating tends to have a finer microstructure and a correspondingly improved hardness. Furthermore, Ta is a metal with excellent ductility but low hardness, whereas Ta₂O₅ is a ceramic material with an inherently higher hardness. Thus, when the two coatings are diluted by the Ti substrate during the laser cladding process, a significant difference in the hardness enhancement of the coatings emerges. Guan et al. [49] used a laser melting additive manufacturing process to fabricate pure Ta and obtained specimens with a hardness greater than 300 HV [49]. Balla et al. [13] performed laser-engineered net shaping to deposit a porous Ta coating on a Ti substrate, resulting in samples with an average hardness of 392 ± 37 HV [13]. The increase in hardness of these Ta coatings was thought to be primarily the result of a solid-solution strengthening effect of the oxygen and nitrogen interstitials. In the current study, a laser was also used as the heating source for the cladding process, and a small quantity of oxygen was detected in the Ta coating. Thus, it is reasonable to assume that the aforementioned solid solution-strengthening mechanism also exists. Since Ta₂O₅ is a ceramic, in addition to its high hardness, it exhibits brittleness. Consequently, it has disadvantages as a coating material [5]. Furthermore, the ceramic phase may also be poorly dispersed in the coating if pre-placement techniques are used [50].

The hardness values of the present Ta samples change smoothly near the interface between the coating and substrate, producing an effect similar to that of a buffer layer, which reduces the stress acting on the coating surface. This reduces the transfer of shear stress to the coating/substrate interface, which in turn extends the life of implant coatings [51, 52]. However, compared with Ta coatings, Ta₂O₅ coatings, which have a higher hardness, have a greater wear resistance [41], which reduces the generation of wear debris and associated implant loosening caused by early-stage micro-motion of the bone-implant interface [53].

A diode laser was used to form single-layer single-pass Ta and Ta₂O₅ coatings on Ti substrates at various laser powers (1000–2000 W) and scanning speeds (3–10 mm/s). The main findings of this study can be summarized as follows.

The melting point of Ta (3017°C) is close to the boiling point of Ti (3287°C), and hence the Ti substrate beneath the molten pool vaporizes during the cladding process. The vapor bubbles have insufficient time to escape the molten pool during the rapid solidification process, and thus pores are formed in the Ta coating close to the interface with the substrate. The porosity tends to decrease with a decreasing specific energy input (E_s) and an increasing laser power.

The melting point of Ta₂O₅ (1882°C) is relatively close to that of the Ti substrate (1667°C). Hence, pore formation is suppressed. However, the thermal expansion coefficient of Ta₂O₅ (4.7 × 10^-6K^-1) is significantly different from that of the Ti substrate (9.41–10.03 × 10^-6K^-1), and thus thermal stress-induced cracking occurs during the cooling and solidification stages.

A high dilution of Ti from the substrate occurs for both the Ta and Ta₂O₅ coatings. The average Ta, Ti, and O contents of the cladded-Ta sample are approximately 35 wt.%, 59 wt.%, and 5 wt.%, respectively. The equivalent contents of the cladded-Ta₂O₅ sample are approximately 18 wt.%, 70 wt.%, and 11 wt.%. Thus, the dilution effect of Ti on the Ta₂O₅ coating is significantly greater than that on the Ta coating.

For both the Ta and Ta₂O₅ samples, the coating hardness is significantly higher than that of the Ti substrate (160–180 HV). Furthermore, the hardness of the Ta₂O₅ coating (580–700 HV) is significantly higher than that of the Ta coating (350–400 HV). In addition, the hardness profiles of the cladded-Ta samples show an obvious smooth downward trend from the coating surface to the substrate, whereas that of the Ta₂O₅ samples remains approximately constant through the coating depth.

Acknowledgments: The authors gratefully acknowledge the financial support provided to this research by the Ministry of Science and Technology of the Republic of China (Taiwan) under Contract No. MOST 106-2622-E-218-007-CC3. The study was also supported in part by MOST 111-2218-E-006-016 and the Chi Mei Medical Center, Republic of China (Taiwan), under Contract No. 13001100317.

Funding: This study was funded by [Ministry of Science and Technology of the Republic of China (Taiwan)] grant number [MOST 106-2622-E-218-007-CC3], [MOST 111-2218-E-006-016] and by [Chi Mei Medical Center, Republic of China (Taiwan)] grant number [13001100317].

Competing Interests: The authors have no relevant financial or non-financial interests to disclose.

Data availability statement: Not applicable.

Author Contributions: All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Yi-Ju Li, Yueh-Hung Hsieh, Wei-Ting Lin and Hong-Chuong Tran. The first draft of the manuscript was written by Yi-Ju Li, Tsung-Yuan Kuo, Chi-Sheng Chien and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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published 01 May, 2024

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Editorial decision: Major Revisions Needed
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19 Jan, 2024
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You are reading this latest preprint version

Comparison of laser cladding properties of tantalum and tantalum pentoxide powders on titanium substrates

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1 Cladding powder preparation

2.2 Sample preparation

2.3 Experimental cladding process

2.4 Morphology, chemical composition, and microhardness

3. Results and discussion

3.1 EDS and XRD analyses of Ta and Ta₂O₅ raw powders

3.2 Surface and cross-sectional morphologies of Ta coatings

3.3 Surface and cross-sectional morphologies of Ta₂O₅ coatings

3.4 Depth and width of coatings

3.5 EDS composition analysis and line scan results

3.6 Microhardness

4. Conclusion

Declarations

References

Status:

Journal Publication

Version 1

Comparison of laser cladding properties of tantalum and tantalum pentoxide powders on titanium substrates

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1 Cladding powder preparation

2.2 Sample preparation

2.3 Experimental cladding process

2.4 Morphology, chemical composition, and microhardness

3. Results and discussion

3.1 EDS and XRD analyses of Ta and Ta2O5 raw powders

3.2 Surface and cross-sectional morphologies of Ta coatings

3.3 Surface and cross-sectional morphologies of Ta2O5 coatings

3.4 Depth and width of coatings

3.5 EDS composition analysis and line scan results

3.6 Microhardness

4. Conclusion

Declarations

References

Status:

Journal Publication

Version 1

3.1 EDS and XRD analyses of Ta and Ta₂O₅ raw powders

3.3 Surface and cross-sectional morphologies of Ta₂O₅ coatings