Core-shell ZrC/Ti2AlC reinforced composite coatings prepared by laser cladding on Zr-alloy substrates

Core-shell ZrC/Ti₂AlC reinforced intermetallic composite coatings were successfully prepared by laser cladding in-situ reaction using TiAl–TiC–Al powder preset on R60702 zirconium alloy surface. As-obtained coatings showed good metallurgical bonding with substrates. Composite coatings mainly contained dendritic ZrC/Ti₂AlC reinforced phase with core-shell structure and intermetallic matrix of Ti_xAl_y and Zr_xAl_y, with small amounts of Ti₃AlC. During laser pool solidification, TiC nucleated at boundary of primary precipitated ZrC dendrite. Al atoms then diffused into TiC outer layer during subsequent solidification process to finally form core-shell structure with ZrC as core and Ti₂AlC as outer layer. Ti₂AlC phase of shell structure improved physical performance between hard ZrC particles and matrix in terms of hardness and thermal expansion coefficient. The maximum hardness of cladding layer (848.8 HV) was 5-fold higher than that of zirconium alloy substrate. Also, no cracking was found inside the coatings or at the junction with substrates. In sum, these findings look promising for future applications of MAX phase composite coatings in nuclear power equipment.     

Microstructure and properties of metal parts remanufactured by laser cladding TiC and TiB2 reinforced Fe-based coatings

Laser cladding process, an efficient surface remanufacturing method, has become a research hotspot in recent years. Herein, in situ titanium carbide (TiC) and titanium diboride (TiB₂) reinforced composite coatings were fabricated on the surface of damaged carbon steel to improve the hardness and wear resistance of remanufactured parts. Effects of addition of 5B₄C and 15Ti (in wt.%) powder on morphology, phase composition, microstructure, and mechanical properties of specimens were comprehensively investigated. Results revealed that milled groove could be effectively filled with composite coating, which formed good metallurgical bonding with the substrate. Furthermore, sequentially precipitated in situ synthesized phases including TiC, TiB₂, Cr₃C₂, Fe₂B, and Fe₃C in composite coating could continuously increase nucleation sites and further refine grains. Moreover, uniformly distributed reinforcements effectively weakened the directivity of heat flow during solidification process and promoted columnar to equiaxed transition. Mechanical properties illustrate that micro-hardness of composite coating with 961.94 HV_0.3 is 4.14 and 5.04 times, and corresponding volume loss is 7.8 and 2.8 less than those of 316 L coating and standard 45 steel, respectively. This study indicates that in situ formed ceramics reinforced composite coating can act as an ideal candidate for remanufacturing damaged parts, and further improve their wear resistance.     

Microstructure and mechanical properties of functionally graded TiCp/Ti6Al4V composite fabricated by laser melting deposition

Crack-free functionally graded TiC particle (TiC_p) reinforced Ti6Al4V (TiC_p/Ti6Al4V) composite was manufactured by laser melting deposition (LMD) technology with TiC volume fraction changing gradually from 0% to 50%. This research focuses on the relationship between the microstructure and mechanical properties (microhardness and tensile properties) of TiC_p/Ti6Al4V composites under different TiC volume fractions. Besides the unmelted TiC particles, the granular and chain shaped eutectic TiC phases are observed in the composite with 5 vol% TiC due to the melting and dissolution of TiC particles into matrix. The granular and dendritic primary TiC phases are obtained in the composite with 10 vol% TiC, while the chain shaped eutectic TiC phases can scarcely be seen. The main reinforcement phases are primary TiC phases when the TiC volume fraction exceeds 15%. (i) The quantity of unmelted TiC particles, (ii) the quantity and size of primary TiC phases and (iii) the porosity of composite increase gradually when the TiC volume fraction increases. The interfaces exhibit good bonding between consecutive layers. The microhardness of the functionally graded TiC_p/Ti6Al4V composite increases gradually with TiC volume fraction increasing. It is attributed to the C element in solid solution and the appearance of eutectic and primary TiC phases. The microhardness at the top layer with 50 vol% TiC is improved by nearly 94% compared with that at the Ti6Al4V side. The tensile strength of TiC_p/Ti6Al4V composite with 5 vol% TiC is enhanced by nearly 12.3% compared with that of the Ti6Al4V matrix alloy. However, both the tensile strength and elongation of composite decrease gradually when the TiC volume fraction exceeds 5%. The reason is that the quantity of brittle unmelted TiC particles and the quantity and size of dendritic TiC phases increase with TiC volume fraction increasing. The fracture mechanism of the TiC_p/Ti6Al4V composite is quasi-cleavage fracture.     

Optimization of microstructure and properties of composite coatings by laser cladding on titanium alloy

Recently, the current technological progress in developing laser cladding technology has brought new approaches in surface modification of titanium alloys. Herein, composite coatings were fabricated by the laser cladding process on Ti811 alloys using a coaxial powder feeding method. A comprehensive study was performed on the laser energy density (L_ed) and CeO₂ content on the structure distribution, microhardness and tribological properties of the coatings. In addition, the growth mechanism of the TiC–TiB₂ structure was studied based on the Bramfitt two-dimensional lattice mismatch theory. The results indicated that the phase composition of the coating mainly contained TiC, TiB₂, Ti₂Ni, and α-Ti. The optimized coating contributed to uniform microstructure distribution and fine grain size when L_ed was 45 J/mm² and the CeO₂ content was 2 wt%, playing an important role in the best forming quality and properties. Besides, the high matching degree of an interface between TiC (111) and TiB₂ (0001) contributed to the TiC–TiB₂ composite structure, which positively influenced the grain size and distribution of TiC. The microhardness and wear resistance of the 2Ce coating was dramatically enhanced due to the fine grain strengthening and dispersion strengthening effects of CeO₂, contributing directly to generate a high average hardness of 811.67 HV_0.5 with a lower friction coefficient.     

Study of TiC/Ni3Al composites by laser ignited self-propagating high-temperature synthesis (LISHS)

TiC/Ni₃Al composites have been obtained in situ by laser ignited self-propagating high-temperature synthesis (LISHS) of an intimate mixture of compacted powders of elemental C, Ti, Ni and Al. Ignition temperature (T_ig) and combustion temperature (T_c) are investigated; the effects of Ni₃Al content on density, phase composition, microstructure of the reaction products and particle size of the synthesized TiC were studied. The results show the density of the products varies with Ni₃Al content, and a maximum value of density appears at 50 wt.% Ni₃Al; TiC and Ni₃Al are the two stable phases after SHS, TiC particle size decreases with the increasing of Ni₃Al content, however, the decreasing of grain size is unobvious when Ni₃Al content is over 60 wt.%.     

Effect of microstructure on the adhesion strength of TiBx coating on Ti6Al4V substrate

TiB_x coatings were deposited on Ti6Al4V and Si (100) wafer substrates by D.C. magnetron sputtering with various target-to-substrate distances (T.S. distances) from 50 mm to 200 mm. The influence of T.S. distance on the microstructure, hardness and adhesion strength of TiB_x coatings and Ti6Al4V substrate system was investigated. Results showed that the microstructure of TiB_x coatings transformed from dense to fibre columnar grain with the increase in T.S. distance, whilst the hardness decreased from 20.9 GPa to 9.4 GPa. The Rockwell-C indentation adhesion strength grade was also improved from HF6 to HF1. An adhesion evaluation factor G, which is related to the mechanical properties and the microstructure of TiB_x coating, is proposed based on the test results. The adhesion strength increased with G, which corresponded well with the results of indentation test. The high-speed rubbing test with a sliding speed of 300 m/s was performed to check the Al-adhesion resistance of the TiB_x coating against Al–hBN seal coating.     

Influence of Y2O3 on the microstructure and tribological properties of Ti-based wear-resistant laser-clad layers on TC4 alloy

Multi-track Ti-based wear-resistant composite coatings were fabricated on TC4 alloy surfaces using laser-clad TC4 + Ni45 + Co–WC mixed powders with different Y₂O₃ contents (0, 1, and 3 wt%). The microstructure, microhardness, and tribological properties of the coatings were characterised using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, electron probe X-ray micro analyser, microhardness tester, and friction and wear testing apparatus. The results showed that the number of cracks on the coating surfaces gradually decreased with the addition of Y₂O₃ and that residual Co–WC powders existed in the coating subsurfaces. The phase composition of the coatings with different Y₂O₃ contents remained unchanged and was mainly composed of reinforcing phases of TiC, TiB₂, Ti₂Ni, and matrix α-Ti. With the addition of Y₂O₃, the coating microstructure was remarkably refined, the direction characteristic of the TiC dendrites obviously weakened, and the nucleation rate significantly increased. When the added Y₂O₃ was 3 wt%, a large amount of TiB₂–TiC-dependent growth composite phases precipitated in the coating. The two-dimensional lattice misfit between (0001)_TiB2 and (111)_TiC was 0.912%, which indicated that TiB₂ and TiC formed a coherent interface. When the amount of Y₂O₃ was increased, the microhardness of the coatings gradually decreased, and the wear volume of the coatings first increased and then decreased. Under the effect of the TiB₂–TiC composite phases, the wear resistance of the 3 wt% Y₂O₃ coating was optimal. The 3 wt% Y₂O₃ coating friction coefficient was the lowest, and the wear mechanism was abrasive wear.     

Repair of spline shaft by laser-cladding coarse TiC reinforced Ni-based coating: Process,microstructure and properties

To repair the surface defects of spline shaft and improve wear resistance, the coarse TiC reinforced Ni-based composite coatings were fabricated on the spline shaft surface by laser cladding with six types of precursors containing Ni45, coarse TiC, and fine TiN powder. The effects of ceramic content and fine TiN addition on the formability, microstructure, and mechanical properties of the coatings were studied comprehensively. In TiC reinforced Ni-based coatings 1–3 without fine TiN addition, the porosity decreased from 20.415 % to 0.571 % with the increase of TiC concentration. The coatings mainly consist of CrB, Cr7C3, Cr23C6, coarse TiC, and γ-Ni. With the addition of fine TiN, the length of the ceramic phases in coatings 1#–3# decreased slightly, while volume fraction and porosity increased. Moreover, the ring-shaped Ti (C, N) phases were also detected at the edges of both undissolved TiC and TiN particles, which improved the bonding force between ceramics and matrix. Besides, these ceramics inhibited the generation of columnar crystals and eliminated the heat-affected zone. The performance test results show that the coating 3# with 30 wt% TiC and 6 wt% TiN exhibits the best wear resistance despite slightly decreased hardness, and its friction coefficient of 0.409 and wear rate of 42.44 × 10⁻⁶ mm³ N⁻¹·m⁻¹ are, respectively, 0.667 and 0.307 times those of the substrate. Based on the additive/subtractive hybrid manufacturing technology, the optimized coatings were ground to obtain the finishing surface, which indicates that the coarse TiC reinforced coating can be employed in repairing the damaged parts.     

Feasibility study of adding buffer layers for the laser deposition of high-ceramic content (TiB + TiC)–Ti coatings using B4C/Ti powders

Wear-resistant coatings have been widely used to improve the tribological properties of titanium-based parts, structures, and tools, such as engine blades, tanker trucks, heat exchangers, and drilling bits, in the aerospace industries, chemical industries, offshore engineering, and oil and gas engineering. In the view of the applications in the fabrication of wear-resistant coatings on titanium substrates, the laser deposition of ceramic reinforced titanium coatings is widely investigated. Reported investigations show that the (TiB + TiC) reinforced titanium matrix composite coatings with high ceramic content can significantly increase the hardness and wear resistance. However, due to the low compatibility between ceramics and titanium, a high ceramic content always leads to a relatively low bonding quality and the generation of cracks and defects. To fabricate the high ceramic content (TiB + TiC)–Ti coatings, this study investigates the feasibility of adding buffer layers for the first time. The phase compositions, microstructures, element compositions, and mechanical properties of the different layers have been analyzed by XRD, SEM, EDS, and instruments to measure hardness and wear resistance. The deposited gradient coatings are free of fabrication defects with good metallic adhesion with titanium substrates. In the center of the top coating layers, the extremely high-volume content of ceramic reinforcements (including the major component of TiB and TiC and the minor component of TiB₂, B₂₅C, and unreacted B₄C) leads to high microhardness and excellent wear resistance. These results suggest that adding buffer layers is a feasible method to fabricate high-ceramic content coatings on titanium-based structures and tools.     

Effect of TiC addition on the microstructure and properties of Ni3Ta–TaC reinforced Ni-based wear-resistant coating

The present study focuses on the surface wear-resistant strengthening technology of the tunnel boring machine disc cutter ring. Ni₃Ta–TaC reinforced Ni-based wear-resistant coatings were synthesized in-situ on the surface of 5Cr5MoSiV steel by laser cladding with pure Ni spherical powder, pure Ta spherical powder and Ni coated graphite. To inhibit coating cracking, TiC powder was added to promote the in-situ formation of TaC. The effect of adding TiC on the microstructure and properties of Ni-based wear-resistant coating has been investigated by experiments and first-principles calculation. The results show that Ni₃Ta and TaC particles are synthesized in-situ in the coating, and small TaC particles are aggregated around TiC. The orientation relationship of TaC (100)//TiC (100) is confirmed by EBSD and TEM. The properties of interface of TaC (100) and TiC (100) are calculated by the first-principles, showing that the C–Ti and Ta–C interface has high adhesion and good stability. The wear resistance of the two coatings is 4 times higher than that of the substrate. The addition of TiC can effectively inhibit the formation of the lath-shaped Ni₃Ta intermetallic compound and cracks, resulting in excellent wear resistance and toughness.     

Nearly dense Ti–6Al–4V/TiB composites manufactured via hydrogen assisted BEPM

Titanium matrix composites reinforced with in situ formed titanium boride whiskers have long aroused significant interest for advanced applications in fields such as aerospace, biomedicine, and armaments. However, processing approaches dedicated to fabricating these composites have usually been limited by the cost-performance dilemma, thereby limiting commercial success. Blended elemental powder metallurgy (BEPM) has historically been the most economical route to produce titanium-based composites. At the same time, the need to reduce undue sinter porosities has imposed complicated and expensive extra thermomechanical steps in BEPM manufacturing. In the present study, nearly dense Ti–6Al–4V-based composites reinforced with in situ synthesized titanium monoborides (TiB) are prepared by simple press-and-sinter hydrogen-assisted BEPM without hot deformation or hot pressing using TiH₂, TiB₂, and master alloy (Al–V) powder blends as starting material. Vacuum sintering of compacted powder blends results in the formation of a dehydrogenated Ti–6Al–4V matrix with excessive porosity and unevenly distributed partially reacted TiB₂ particles. Such an inappropriate pre-sintered microstructure can be completely transformed into low-porosity uniform Ti–6Al–4V/TiB composites with tailored grains by using hydrogenation and milling of pre-sintered material into hydrogenated pre-alloyed powders and, finally, by using these powders in a second press-and-sinter processing step. The useful influence of hydrogen as a temporary alloying element on microstructure formation is discussed. The densification of hydrogenated powder compacts upon vacuum heating, and the hydrogen emission from the material is studied via dilatometric tests. The evolution of microstructure and phase composition during processing steps was investigated by scanning electron microscopy and x-ray diffraction. Compressive tests were used to evaluate the mechanical properties of materials produced after the first and second sintering. The results show that hydrogen-assisted BEPM can be a cost-effective route for in situ fabrication of Ti–6Al–4V/TiB composites with reliable mechanical properties.     

Wetting,reactivity, and phase formation at interfaces between Ni–Al melts and TiB2 ultrahigh‐temperature ceramic

The wetting, reactivity, and phase formation at the liquid Ni–Al/TiB₂ ceramic interfaces have been investigated at the temperatures close to the Ni–Al liquidus line. The wetting kinetics has been studied by the sessile drop technique utilizing liquid drop dispension and high‐speed high‐resolution video imaging. It is established that the wetting behavior changes from a nonreactive for the Al‐rich melts to a dissolution‐reactive for the Ni‐rich melts. For the Ni concentration ≥40 at.%, TiB₂ precipitates are found in the solidified Ni–Al droplets after the high‐temperature interaction of the melts with TiB₂ substrates. Besides, new (Al,Ti)Ni₃ and (Al,Ti)₂Ni₂₁B₆ phases are formed due to dissolution of TiB₂ ceramic in Ni‐rich melts and subsequent solidification.     

Rapid synthesis of Ti3AlC2/TiB2 composites by the spark plasma sintering (SPS) technique

Dense Ti₃AlC₂/TiB₂ composites were successfully fabricated from B₄C/TiC/Ti/Al powders by spark plasma sintering (SPS). The microstructure, flexural strength and fracture toughness of the composites were investigated. The experimental results indicate that the Vickers hardness increased with the increase in TiB₂ content. The maximum flexural strength (700 ± 10 MPa) and fracture toughness (7.0 ± 0.2 MPa m^1/2) were achieved through addition of 10 vol.% TiB₂, however, a slight decrease in the other mechanical properties was observed with TiB₂ addition higher than 10 vol.%, which is believed to be due to TiB₂ agglomeration.     

Interfacial microstructure evolution and mechanical properties of B4C-based composite joints bonded with Ti foil

The interfacial microstructure and mechanical properties of B₄C-SiC-TiB₂ composite joints diffusion bonded with Ti foil interlayer were investigated. The joints were diffusion bonded in the temperature range of 800–1200?°C with 50?MPa by spark plasma sintering. The results revealed that robust joint could be successfully obtained due to the interface reaction. B₄C reacted with Ti to form nanocrystalline TiB₂ and TiC at the interface at 800–1000?°C. Both the reactions between SiC and Ti and between TiB₂ and Ti were not observed during joining. A full ceramic joint consisted of micron- and submicron-sized TiB₂ and TiC, accompanied with the formation of micro-crack, was achieved for the joint bonded at 1200?°C. Joint strength was evaluated and the maximum shear strength (145?±?14.1?MPa) was obtained for the joint bonded at 900?°C. Vickers hardness of interlayer increased with increasing the joining temperature.     

Microhardness and wear resistance of Al2O3-TiB2-TiC ceramic coatings on carbon steel fabricated by laser cladding

Al₂O₃-TiB₂-TiC ceramic coatings with high microhardness and wear resistance were fabricated on the surfaces of carbon steel substrates by laser cladding using different coating formulations. The microstructures of these ceramic coatings with the different coating formulations were investigated using X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer. The wear resistance and wear mechanism were analyzed using Vickers microhardness and sliding wear tests. The results showed that when the amount of independent Al₂O₃ was increased to 30%, the ceramic coatings had a favorable surface formation quality and strong metallurgical bond with the steel matrix. The cladding layer was uniformly and densely organized. The black massive Al₂O₃, white granular TiB₂, and TiC distributed on the Fe substrate significantly increased the microhardness and wear resistance. The laser cladding ceramic coating had many hard strengthening phases, and thus resisted the extrusion of rigid particles in frictional contact parts. Therefore, the wear process ended with a “cutting-off” loss mechanism.     

Characterization of the structure of TiB2/TiC nanocomposite powders fabricated by high-energy ball milling

TiB₂/TiC nanocomposite powders were successfully prepared by high-energy ball milling of the powder mixtures of Ti and B₄C. X-ray diffraction analysis showed that the TiC phase was not produced until the milling time was up to 24 h and only a minimal amount of TiB₂ was generated, even after 48 h of milling. The critical grain size of Ti milled for the reaction between Ti and B₄C was 31.2 nm. Transmission electron microscopy clearly indicated that the resulting powder mixture obtained after milling for 48 h and annealing at 800 °C for 30 min was composed of nanosized TiC and TiB₂ particles.     

Synthesis of Ti-Al-based materials by thermal explosion

Ti-Al-based materials reinforced with TiC and TiB₂ particles were prepared by thermal explosion in compacted (Ti + 0.3B₄C) + xAl and (Ti + 3Al) + yB₄C blends. The structure/properties of synthesized materials were characterized by XRD, SEM, and mechanical testing. An increase in x was found to affect the microstructure of products (lower grain size) and to have no influence on reaction temperature. An increase in y was found to decrease reaction temperature and to change the structure/composition of products toward better viscoelastic behavior.     

Effect of Ti content on the microstructure and mechanical properties of laser clad Ti/B4C/dr40-based composite coatings on shaft parts surface

As a transmission part, the service life of the shaft parts directly affects the machining efficiency and economic benefit, and requires higher surface hardness and wear resistance. In this study, the Ti/B₄C/dr40 composite powder was cladded on the shaft part surface via laser cladding to improve the microhardness and wear resistance. The microstructure evolution and phase structure were analyzed to reveal the strengthening mechanism of Ti and B₄C on dr40 coating. The Ti/B₄C/dr40 composite coating with low defects and good interface metallurgical bonding quality between coating and substrate was prepared on the 45# steel shaft part. The results show that the main phase in the Ti/B₄C/dr40 composite coating is TiC, TiB₂, Cr₂C₃, (Ti, Cr) C, (Ti, Cr, Fe, Ni) (C, B). With the addition content of Ti increasing, the grain densifies, the sieve-reticular structure and small strip phase at grain boundary and intergranular area change as massive phase. Moreover, the microhardness improves up to 2.05 times than that of dr40 coating. The in-situ synthesis of carbides and borides are evenly distributed in the coating, which improves the deformation resistance of the coating. In addition, the precipitation and solid solution strengthening caused by reinforcement phase also enhanced matrix strength for supporting reinforcement phases, improving the coating wear resistance.     

Interfacial structures and strengthening mechanisms of in situ synthesized TiC reinforced Ti6Al4V composites by selective laser melting

The in-situ nanoscale TiC particles reinforced Ti6Al4V composites was prepared by selective laser melting (SLM) from the mixture of Ti6Al4V alloy powders and graphene powders, the microstructure and interface bonding of the composites were studied. The composites were mainly composed of α, α' martensite and α+β structures. More TiC were formed in the overlapping regions than that in the molten pool, the solidification rate in overlapping regions was slow, which was beneficial to TiC nucleation and growth. The TiC and Ti matrix displayed following orientation relationships: axis [0 0 1]_β-Ti∥[-1 -1 1]_TiC∥[0 -1 1 0 ]_α-Ti, lattice plane (2 2 2)_TiC //(0 0 0 2)_α-Ti, lattice plane (1 1 1)_TiC//(0 0 0 2)_α-Ti, lattice plane (1 1 1)_TiC//(1 0 -1 0)_α-Ti. The TiC and Ti matrix have a small degree (6.2%) of mismatch between (1 1 1)_TiC and (0 0 0 2)_α-Ti, and the semi-coherent interface was occurred. TiC preferentially nucleated and grew up along its (1 1 1) plane. The situ synthesized TiC was added into the Ti6Al4V alloy, refined the grains, and increased the microhardness of the alloy. The microhardness of the composites was 13.6% higher than that of Ti6Al4V alloy. The TiC effectively pinned the dislocations and grain boundaries were responsible for the enhanced mechanical properties of the composites.     

Effect of Si content on the microstructure and properties of Ti–Si–C composite coatings prepared by reactive plasma spraying

In this study, Ti–Si–C composite coatings were synthesized via plasma spraying of agglomerated powders prepared by a spray drying/precursor pyrolysis technology using Ti, Si, and sucrose powders. The influence of Si content, ranging from 0 wt% to 24 wt%, on the microstructure, mechanical properties, and oxidation resistance of the composite coatings was investigated. Results show that the phase composition of the Ti–Si–C composite coatings changes with the increasing Si content. The coatings without Si addition consist of TiC and Ti₃O; the coatings with 6–18 wt% Si are composed of TiC, Ti₅Si₃, and Ti₃O; the coatings with Si content of 24 wt% form only TiC and Ti₅Si₃ phases. As the Si content increases, the hardness of the Ti–Si–C composite coatings increases first and then decreases, depending on the intrinsic hardness of the ceramic phases, the brittleness of Ti₅Si₃, and the defects such as pores and cracks. The Ti–Si–C composite coatings have high wear resistance due to the in-situ synthesized high-hardness TiC and Ti₅Si₃. Owing to the high brittleness of Ti₅Si₃, the increasing Si content leads to higher wear volume loss at room temperature, which can be partially improved in high-temperature wear tests. The oxidation resistance of Ti–Si–C composite coatings increases with the increase of Si content, and the higher the oxidation temperature, the more obvious the influence of the Si addition on oxidation resistance.