Laser Cladding Fabrication of B₄C-Reinforced Titanium Matrix Composites: Wear Resistance and Corrosion Performance

Abstract

This study involves the addition of B₄C particles to TC4 powder to fabricate B₄C-reinforced titanium matrix composite coatings on an AISI 304L substrate using a laser cladding process. The effects of B₄C addition (0–12 wt.%) on microstructure, microhardness, wear, and corrosion performance were systematically investigated. Results indicate that the composite coating with 9 wt.% B₄C exhibits optimal properties, achieving a peak microhardness of 600 HV_0.2 and a wear rate of 2.82 × 10⁻⁴ mm³/N·m, representing a 58.22% reduction compared to the pure TC4 coating. Electrochemical tests in 3.5 wt.% NaCl solution reveal a significant positive shift in corrosion potential and reduced corrosion current density with increasing B₄C content, confirming enhanced corrosion resistance, and the improved performance is attributed to grain refinement and dispersion strengthening by B₄C particles. This work provides a feasible strategy for enhancing the surface properties of 304L stainless steel under demanding wear and corrosive environments.

1. Introduction

AISI 304 stainless steel (SS 304L) is extensively employed in critical sectors such as biomedical implants, aerospace components, and marine structures owing to its outstanding corrosion resistance, good heat resistance, and oxidation stability [1,2,3]. However, its relatively low surface hardness and poor wear resistance severely limit its performance in applications involving frequent friction, abrasive environments, or demanding mechanical loads. To extend the service life and expand the application scope of 304L components, it is imperative to improve their surface properties through advanced modification techniques. Laser cladding stands out as an effective technique due to its characteristics of high energy density, low dilution rate, and rapid heating and cooling rates [4,5,6,7], in which an alloying layer with good metallurgical bonding at the interface can be acquired over the substrate, which is regarded as a suitable way to fabricate enhanced layers on 304L substrate.

Ceramic-reinforced metal matrix composites (MMCs) combine the toughness and ductility of the metal matrix with the high hardness and strength of ceramic reinforcements, yielding synergistic properties unattainable by conventional alloys. These include high specific strength, specific stiffness, low thermal expansion, and superior wear and temperature resistance [8,9,10]. Among various MMCs, titanium matrix composites (TMCs) are particularly promising for advanced aerospace, automotive, and biomedical applications due to their exceptional strength-to-weight ratio, corrosion resistance, and biocompatibility [11,12,13]. A key challenge lies in further enhancing their surface mechanical properties, such as hardness and wear resistance, to meet more demanding operating conditions. Boron carbide (B₄C) is recognized as the third hardest ceramic material globally [14,15], surpassed only by diamond and cubic boron nitride (CBN). It retains a high hardness of 9.3 on the Mohs scale even at elevated temperatures [16,17]. B₄C exhibits a low density of 2.52 g/cm³ and possesses a high melting point, making it highly suitable for incorporation via laser cladding process [18,19,20]. Bai et al. identified an optimal B₄C content range that significantly improves microhardness, fracture toughness, and wear resistance in coatings [21]. Coatings containing an appropriate amount of B₄C (not exceeding 15 wt.%) have demonstrated outstanding overall mechanical properties. Similarly, Xu et al. reported that adding 2% B₄C nanoparticles to an IN625 matrix via laser cladding resulted in an ~86% reduction in wear rate, despite a slight increase in the coefficient of friction [22]. However, there is little research data that can be found about adding B₄C particles to the TC4 powder, and the corresponding weight ratio of its addition is not clear. It is worth noting that the C element in B₄C is beneficial to the formation of carbide hard phases, but is also prone to forming cracks [23,24]. Alexander Golyshev et al. prepared Ti-6Al-4V/BC composite materials containing boron carbide (BC) powder on a titanium alloy substrate using selective laser melting (SLM) technology and analyzed the influence of different weight percentages (1%, 5%, and 10%) on the composite material properties. The results demonstrated that increasing the BC content led to enhanced hardness and crack propagation resistance of the material. Significantly, at a BC content of 10%, the composite achieved its peak hardness of approximately 372.0 HV_0.3, with wear resistance approximately 4.2 times higher than that of samples devoid of BC. Furthermore, the microstructural analysis revealed the formation of a heterogeneous structure and issues related to phase transformations associated with regular arrangement in each newly deposited layer [25]. Previous research outcomes concerning B₄C furnish a well-grounded conceptual framework and a promising launchpad for the present investigation.

Hence, the present work employed laser cladding technology to fabricate B₄C-reinforced TC4 titanium matrix composite coatings on an AISI 304L stainless steel substrate. The research focuses on the systematic investigation of the effect of B₄C addition (at 0, 3, 6, 9, and 12 wt.%) as a secondary phase on the microstructure, microhardness, wear resistance, and corrosion behavior in a 3.5 wt.% NaCl solution of the coatings. The primary objectives are to elucidate the structure–property relationships between B₄C content and the overall coating performance, to identify an optimized B₄C content range that achieves high hardness, superior wear and corrosion resistance without significant defects, and to reveal the underlying wear failure mechanisms of the composite coatings. This work aims to provide both experimental evidence and theoretical guidance for developing high-performance surface protective coatings on 304L stainless steel, suitable for demanding wear and corrosive environments.

2. Experimental Procedure

2.1. Materials and Laser Cladding Process

SS AISI 304L cuboid specimens with dimensions of 120 mm × 100 mm × 15 mm were utilized as the parent material for laser cladding. TC4 powders, having a particle size range of 35–100 µm, were chosen as the primary raw material, with their detailed chemical composition presented in

Table 1. Chemical composition of TC4 powders (wt.%).

Element	Al	V	N	Fe	O	Ti
Mass fraction	6.36	4.06	0.0112	0.05	0.077	Bal.

. The selected cladding materials are B₄C powders and TC4 powders, with their microscopic morphologies shown in Figure 1. To make a homogeneous mixture, the metal matrix composite powders were uniformly mixed in a planetary ball mill (Nanjing Nanda Instrument Co., Ltd., Nanjing, China). The ball milling process parameters were as follows: a ceramic ball made of zirconia (ZrO₂) with a diameter of 5 mm, a ball-to-powder ratio of 10:1, a speed of 100 r/min, and a milling time of 2 h. Five kinds of powder mixtures with different mass ratios of B₄C and TC4 powders were used in the experiments, as listed in

Table 2. Mass fraction (wt.%) of different powder mixtures.

Specimen Number	Specimen Information	B4C/wt.%	TC4/wt.%
S1	Pure TC4	0	100
S2	TC4@3B4C	3	97
S3	TC4@6B4C	6	94
S4	TC4@9B4C	9	91
S5	TC4@12B4C	12	88

. The powder mixtures were designated TC4, TC4@3B₄C, TC4@6B₄C, TC4@9B₄C, and TC4@12B₄C, respectively, based on the incremental mass percentages of B₄C incorporated.

2.2. Laser Cladding Process

Before laser cladding, the surface of the substrate was mechanically polished and cleaned with ethanol to obtain a flat and smooth surface as well as avoid oxides and foreign inclusions. The TC4/B₄C composite coatings were fabricated using the LSJG-GQ-3200 laser cladding system (Nanjing Zhongke Raycham Laser Technology Co., Ltd., Nanjing, China) composed of an IPG optical fiber system and a powder feeder, and the laser heat source exhibits a Gaussian distribution, meaning that the heat flux density is non-uniform, with a high energy concentration near the center of the beam spot and diminishing energy further away from the center. The peak power achievable is up to 3200 watts, and the wavelength operates at 1080 ± 10 nm. The optimization of laser cladding parameters was applied as laser spot diameter of 4 mm, scanning speed of 8 mm/s, laser power of 2000 W, powder feeding rate of 1.5 g/min, and overlapping rate of 50%. Notably, during the laser cladding process, the 99.99% purity argon gas was blown into the molten pool for protection from oxidation with a gas flow rate of 4 L/min. A schematic representation of the laser cladding process is illustrated in Figure 2.

2.3. Mechanical Property Characterization

The Vickers hardness of each coating was measured using HVS-1000ZCM-XY microhardness indenter (Shanghai Suoyan Testing Instrument Co. Ltd., Shanghai, China) with a 200 g load and 15 s dwell time. The microhardness measurements of each specimen were taken at different locations on the cladding layer, and the average value of ten measurement results was employed. In self-made seawater (prepared seawater was obtained by dissolving a defined quantity of sea salts into deionized water to reach a 2–10 wt.%.) medium, the tribological properties of different coatings were evaluated on MFT-5000 tribometer (Rtec Co., San Jose, CA, USA) for 30 min using a normal load of 15 N, a sliding distance of 8 mm and a sliding frequency of 1 HZ. A 9 mm-diameter Si₃N₄ ball (Ra ≤ 0.05 µm) was applied as the counter-bodies. Post-experiment, the wear volume was measured by White Light Interferometer (MFP-D, RTEC Instruments, San Jose, CA, USA), and the worn surface morphology was characterized using a scanning electron microscope (SEM, Thermo Fisher Scientific, Waltham, MA, USA) to reveal the wear mechanism of varying coatings.

2.4. Electrochemical Test

To investigate the corrosion behavior of various coatings at room temperature, all samples were submerged in a 3.5 wt.% NaCl solution. All electrochemical experiments were carried out on an electrochemical workstation (CHI660E, Shanghai Chenhua Instrument (CH Instruments), Shanghai, China) using a conventional three-electrode electrolytic cell consisting of platinum as a counter electrode, a saturated calomel electrode (SCE) as a reference electrode, and the test sample as the working electrode. The exposed area of the working electrode was 1.44 cm², and the non-working face was sealed by acrylic resin powder. Before electrochemical impedance spectroscopy (EIS) tests, all samples were immersed in NaCl solution for over 1000 s to obtain a stable open-circuit potential (OCP). The frequency ranged from 10⁵ to 10⁻² Hz using a 10 mV (vs. SCE) sinusoidal potential modulation. Afterward, the potentiodynamic polarization tests were conducted from a potential range of −1 V to 1 V (vs. SCE) at a scanning rate of 0.5 mV·s⁻¹. Finally, the impedance spectra were analyzed and fitted using the ZSimpWin 3.60 software. Notably, all electrochemical tests were conducted three times to confirm their reproducibility.

3. Results and Discussion

3.1. Surface Morphology

Figure 3 illustrates the surface morphologies of composite coatings containing varying amounts of B₄C. Due to different physical properties including thermal expansion coefficient, specific heat capacity, and mutual solubility of the layer and the substrate, when pure TC4 coating was laser cladding on the surface of SS AISI 304L substrate, some micro-cracks can be observed on the surface of the coatings. The introduction of a small quantity of B₄C reinforcement (3.0 wt.%, 6.0 wt.%, and 9.0 wt.%) into the TC4 powder resulted in composite coatings with no discernible micro-cracks on their surfaces. This phenomenon can be explained by the fact that mixing a small amount of B₄C can not only refine the grains and improve the fluidity of the solution but also reduce the surface tension of the molten pool, which is beneficial to diminish the tendency to generate cracks. However, with the incorporation of 12.0 wt.% B₄C, significant cracks can be observed on the surface of the composite coatings. Consequently, the TC4@12B₄C sample was not included in subsequent analyses.

3.2. Cross-Sectional Micrograph and Microstructure

As shown in Figure 4, a typical specimen of TC4@9B₄C composite coatings was selected for characterization through SEM cross-sectional micrographs and microstructural analysis. From Figure 4a, it can be distinctly observed that the clad region is composed of the cladding layer, dilution zone, Heat-Affected Zone (HAZ), and substrate. The SEM cross-sectional image after laser cladding reveals no evident cracks or pores, signifying the absence of any severe defects. A small amount of unmolten powder adheres to the upper surface of the cladding layer, which appears overall flat and smooth. Moreover, the interface between the cladding layer and the substrate exhibits tight and uniform bonding, indicating excellent metallurgical adhesion throughout. In Figure 4b–d, microstructures at different interfaces—upper, middle, and lower parts—are displayed for the cladding layer. At the top interface of the cladding layer in Figure 4b, a dense mixture of columnar grains, equiaxed grains, and dendritic grain structures is apparent, with relatively smaller grain sizes due to the high undercooling caused by rapid laser solidification, which restricts grain growth. As shown in Figure 4c,d, moving towards the substrate (at the middle and lower interfaces), microstructural features such as compositional segregation, grain coarsening, and precipitation or dissolution of secondary phase particles are observed, which are closely related to the decreasing temperature gradient during the laser cladding process. Figure 4e,f illustrate dispersed unmolten B₄C particles embedded within the Ti alloy matrix, forming a characteristic metal matrix composite structure. Notably, no significant in situ formation of TiC and TiB₂ phases was detected. This could potentially stem from two factors: on one hand, the excessively large temperature gradient during laser cladding might not have been sufficient to allow for a complete reaction, thus leaving inadequate time for the generation of TiC and TiB₂. On the other hand, the molar ratio of Ti to the B₄C precursor may not have reached the optimal proportion necessary for generating TiC and TiB₂, leading to difficulties in the reaction proceeding or insufficient production of the targeted compounds. In addition, the cross-sectional measurements for the dimension of the TC4 composite coatings are presented in

Table 3. Cross-sectional dimensions of laser-cladded TC4/B₄C composite coatings.

Specimen Number	Specimen Information	Width (mm)	Depth (mm)
S1	Pure TC4	4.50 ± 0.15	1.85 ± 0.10
S2	TC4@3B4C	4.35 ± 0.15	1.90 ± 0.10
S3	TC4@6B4C	4.25 ± 0.15	1.95 ± 0.10
S4	TC4@9B4C	4.05 ± 0.15	2.05 ± 0.10

. It can be observed that as the B₄C content increases from 0 wt.% to 9 wt.%, the coating width decreases slightly from 4.50 mm to 4.05 mm, while the coating depth increases from 1.85 mm to 2.05 mm. This trend can be attributed to the influence of B₄C particles on the melt pool dynamics. The addition of B₄C, which has a significantly higher melting point than TC4, increases the overall viscosity of the molten pool and alters its surface tension. This results in reduced lateral flow (leading to narrower width) and enhanced penetration into the substrate (leading to greater depth) due to improved energy absorption and Marangoni convection effects. These dimensional changes are consistent with the microstructural observations in Figure 4, where a more refined and denser structure is evident with increasing B₄C content, further validating the role of B₄C in modifying the solidification behavior.

3.3. Microhardness Analysis

To evaluate the effect of the content of B₄C as reinforcement particles on the microhardness of the composite coatings, the microhardness distribution along the depth direction was measured, as shown in Figure 5. It was found that the microhardness of the coatings was positively correlated with the B₄C content. The microhardness of the substrate (SS AISI 304L) is only around 270 HV_0.2. However, the microhardness at the top of the TC4, TC4@3B₄C, TC4@6B₄C, and TC4@9B₄C samples are around 320 HV_0.2, 440 HV_0.2, 550 HV_0.2 and 600 HV_0.2, respectively. In particular, the microhardness of TC4@9B₄C increased by 122.2% compared to the substrate. This enhancement is attributed primarily to the intrinsic hardness of B₄C particles and grain refinement induced by laser processing. While some studies suggest that trace in situ formation of TiC/TiB₂ phases may contribute to hardening [26], their presence was not definitively confirmed in the microstructure. Thus, the observed mechanical improvement is likely dominated by B₄C dispersion strengthening and microstructural refinement, rather than in situ reaction phases.

3.4. Wear Behavior

The friction coefficients, three-dimensional worn morphologies, and wear volumes of titanium matrix composite coatings with different B₄C contents prepared by laser cladding are shown in Figure 6. Figure 6a presents the real-time friction coefficient curves, revealing that the wear process consists of two distinct stages: a running-in period and a steady-state wear period. Consistent with established literature [27,28], the running-in phase (approximately 0–100 s) exhibits higher fluctuations and an overall increasing trend in the friction coefficient. After this period, the curves stabilize, indicating the transition to steady-state wear. This stabilization may be further promoted by the seawater test medium, where a surface-tension water film between the grinding ball and the coating must be ruptured before full contact, thereby damping friction variations. As shown in Figure 6b, the pure TC4 coating exhibits the highest average friction coefficient, in accordance with the intrinsically poor wear resistance of titanium alloys. With the addition of B₄C, the microhardness of the coatings increases significantly, leading to a clear downward trend in the friction coefficient. The composite with 9.0 wt.% B₄C achieves the lowest friction coefficient of 0.5019, representing a 17.44% reduction compared to pure TC4. This improvement is attributed not only to the dispersion strengthening and grain refinement induced by B₄C but also to the possible formation of a protective boron-rich oxide layer at the friction interface under localized high temperatures, which further mitigates wear. Figure 6c displays the three-dimensional worn morphology of the TC4@9B₄C coating, used to calculate the wear volume. The corresponding volume wear rates are plotted in Figure 6d, showing a variation trend consistent with that of the friction coefficient. At 9.0 wt.% B₄C, the wear rate reaches a minimum of 2.82 × 10⁻⁴ mm³·N⁻¹·m⁻¹, which is 58.22% lower than that of the pure TC4 coating. The enhanced wear performance is primarily due to the role of B₄C as a dispersed reinforcing phase. The hard B₄C particles effectively pin dislocations in the TC4 matrix, increasing the critical shear stress for dislocation motion and thereby improving yield strength, hardness, and resistance to plastic deformation. Additionally, the high melting point of B₄C (about 46.7% higher than that of TC4) reduces the molten-pool dilution rate during cladding, contributing to a more refined and reinforced microstructure. In summary, the incorporation of B₄C effectively improves the wear resistance of TC4-based coatings through combined mechanisms of dispersion strengthening, grain refinement, and possible surface tribo-oxidation, resulting in simultaneously lower friction coefficients and significantly reduced wear rates.

To elucidate the underlying wear mechanisms, a detailed analysis of the worn surfaces across titanium matrix composite coatings with varying B₄C contents was conducted. The results indicate that material removal predominantly occurred through plastic deformation and delamination wear, with accompanying abrasive grooves. As shown in Figure 7a, the pure TC4 coating surface exhibited fragmented wear debris and pronounced delamination features. With the introduction of B₄C reinforcement, the wear morphology shifted toward delamination-dominated damage, while the severity of abrasive grooves was notably reduced, as evident in Figure 7b–d. The enhanced microhardness resulting from B₄C addition effectively delayed the initiation and propagation of delamination, thereby improving overall wear resistance; this finding is consistent with the tribological test results. Notably, at the optimal B₄C content of 9 wt.%, Figure 7d reveals the emergence of micro-cracks within the coating, suggesting that while B₄C significantly enhances hardness and wear performance, higher ceramic content may promote localized brittleness under repeated sliding stress.

3.5. Electrochemical Behavior

To investigate the effect of B₄C addition on the corrosion resistance of TC4 coatings on 304L substrate, the samples were detected by electrochemical tests in 3.5 wt.% NaCl solution. Figure 8 shows the potentiodynamic polarization curves of different coatings, and the corresponding electrochemical parameters, including corrosion potential (E_corr) and corrosion current density (I_corr), can be obtained through Tafel extrapolation, as listed in

Table 4. Electrochemical parameters of different samples.

Sample	Ecorr, V	Icorr, A/cm2	Rp, Ω·cm2
Pure TC4	−0.355	7.98 × 10−6	5952.5
TC4@3B4C	−0.327	7.28 × 10−6	7156.5
TC4@6B4C	−0.279	5.20 × 10−6	9497.3
TC4@9B4C	−0.182	3.19 × 10−6	14,230.9

. As can be seen, the E_corr of TC4 coating, TC4@3B₄C, TC4@6B₄C and TC4@9B₄C composite coatings is about −0.355 V/SCE, −0.327 V/SCE, −0.279 V/SCE and −0.182 V/SCE, while the I_corr of which is 7.98 × 10⁻⁶, 7.28 × 10⁻⁶, 5.20 × 10⁻⁶ and 3.19 × 10⁻⁶ A/cm². In general, the corrosion potential can reflect the corrosion difficulty of the material, and the higher the value, the better the corrosion resistance of the material [29]. Higher corrosion current density means lower corrosion resistance and faster corrosion speed [30]. It can be found that a higher E_corr value can be obtained with the increase in B₄C addition (TC4 < TC4@3B₄C < TC4@6B₄C < TC4@9B₄C). Accordingly, the TC4@9B₄C sample exhibits superior corrosion resistance.

To further investigate the corrosion behavior of the TC4/B₄C composite coatings, EIS measurement was carried out to analyze the corrosion-inhibiting effect, as depicted in Figure 9. Figure 9a shows the Nyquist diagram of different samples, with the capacitance loop in the low-frequency region inserted in it. As we all know, the radius and shape of Nyquist plots can reflect the properties of the passive film and the electrochemical process [31,32]. A higher Z modulus at a lower frequency and a larger radius of the capacitive loop mean a lower corrosion rate. Thus, the corrosion resistance was: TC4@9B₄C coatings > TC4@6B₄C coatings > TC4@3B₄C coatings > Pure TC4 coating, which was consistent with the results of the potentiodynamic polarization curve, as shown in Figure 9b. Moreover, as shown in Figure 9c, it can be observed from the Nyquist plots that all the samples perform a single-capacitor circuit, which means that the corrosion on the surface of all the laser-modified samples is mainly controlled by charge transfer, which is transferred to the electrolyte through the coating surface. For further interpretation of the EIS results, measured data were fitted using an equivalent circuit presented in Figure 9d, which describes the electrical components of the working electrode and the physical parameters of the solution system. The R_s represents the resistance of the electrolyte; R_f represents the thin film resistance formed on the coating surface, acting as an accumulated barrier between the metal and the aggressive medium interface; R_ct and R_st indicate the high charge transfer resistance and the charge transfer resistance of the substrate, respectively. The surface properties of the 304L substrate were improved, and R_ct was greatly improved by laser cladding titanium alloy composites. The total resistance of the system is represented by the polarization resistance R_p, which is a combination of R_f and R_ct. In addition, the three non-ideal capacitors indicate a constant phase element generated by the membrane/solution interface, a constant phase element generated by the coated metal and the surrounding film, and the capacitor CPE generated by the surface inhomogeneity between the coated metal and the substrate material, respectively. Y₀₁ and Y₀₂ correspond to the amplitude of change in Q₁ and Q₂ constant phase elements between film/solution and metal/film, respectively. According to

Table 5. Equivalent circuit parameters for laser cladding different coatings on 304L substrate.

Sample	Rs (Ω.cm2)	CPE1	Rf (Ω.cm2)	CPE2	Rct (Ω.cm2)	Cap × 10−4	Rst (Ω.cm2)	χ2 × 10−3
		Y01 × 10−4 (Ω−1cm−2sn) n1		Y02 × 10−4 (Ω−1cm−2sn) n2
Pure TC4	15.79	3.730 0.65	23.41	2.016 0.81	7810	2.954	10,642	6.391
TC4@3B4C	13.40	3.474 0.65	43.4	4.087 0.94	19,060	1.381	10,816	1.172
TC4@6B4C	14.89	1.305 0.64	77.46	2.130 0.75	27,400	1.325	13,630	2.738
TC4@9B4C	14.42	0.195 0.74	80.31	1.491 0.78	27,750	1.740	18,842	2.821

, the values of dispersion coefficients n₁ and n₂ are less than 1, indicating that surface defects are caused by roughness, porosity, and hard phases. It can be found that the TC4@9B₄C composite coatings show the highest R_st value. The R_f value is in a fluctuating state, which may be due to the inconsistent surface composition of part of the resistance and the different hindrance effects of the dense oxide film formed on charge transfer. However, compared with the samples without the enhanced phase, the overall film resistance of the other samples is greatly reduced. The increase in Y₀₁ and Y₀₂ indicated that the water resistance of the sample surface was improved with the addition of the reinforcing phase. In addition, the dispersion coefficient n also shows an increasing trend, which is consistent with the improvement of corrosion protection behavior of metal surfaces by laser cladding coating in aggressive media. χ² values are all slightly higher than 1 × 10⁻³, further verifying the minimum error margin in electrochemical circuit fitting.

To further validate the corrosion behavior and the role of the B₄C reinforcing phase, EDS elemental mapping was conducted on the TC4@9 B₄C composite coating after the potentiodynamic polarization test, as shown in Figure 10. The Ti, Al, and V maps exhibit uniform distribution across the analyzed area, indicating that the TC4 matrix maintained its structural integrity without significant elemental dissolution or segregation during corrosion. In contrast, the B and C maps reveal localized enrichment at specific sites, corresponding to the positions of undissolved B₄C particles. This confirms that the B₄C reinforcing phase remained stable under the corrosive conditions and did not undergo complete dissolution or detrimental interfacial reactions. The presence of intact B₄C particles after corrosion suggests that they may act as physical barriers that hinder the propagation of corrosion pathways, contributing to the enhanced corrosion resistance observed for the TC4@9 B₄C coating. These EDS findings are consistent with the electrochemical results discussed above.

4. Conclusions

In this study, TC4/B₄C composite coatings were successfully fabricated on an AISI 304L substrate using laser cladding technology to improve the mechanical properties, wear, and corrosion resistance of the AISI 304L substrate. From the above results and analysis, the results of the work are summarized as follows:

(1)

The addition of B₄C makes the micro-cracks disappear on the pure TC4 coating on the surface of the 304L substrate. When the addition amount is more than 12.0 wt.%, significant cracks were observed on the surface of the titanium matrix composite coatings.

(2)

The microhardness of the TC4/B₄C composite coatings saw a substantial improvement over that of pure TC4 coatings, a phenomenon attributable to the dual role of B₄C in both reinforcing and refining the microstructure of the cladding layer. When the addition of B₄C was 9 wt.%, the microhardness of titanium matrix composite coatings reached 600 HV_0.2, significantly increased by 122.2% compared to the substrate.

(3)

For the case of 9 wt.% B₄C into TC4 powders, the friction coefficient of the titanium matrix composite coatings was about 0.5019, and the wear rate was 2.82 × 10⁻⁴ mm³/N·m, which is 58.22% lower than that of the coating without B₄C addition. With the increasing addition of B₄C, the groove phenomenon caused by abrasive wear of the coatings was weakened.

(4)

The electrochemical tests showed the corrosion resistance of the titanium matrix composite coatings in 3.5 wt.% NaCl solution was dramatically enhanced with the increase in B₄C addition. After adding B₄C, the self-corrosion potential of the composite coatings was significantly higher than that of the pure TC4 coating, and the self-corrosion current density of TC4@9B₄C composite coatings decreased to 3.19 × 10⁻⁶ A/cm².