Ti6Al4V Matrix Composites Research Articles

Laser powder bed fusion additive manufacturing of Ti6Al4V-matrix composite with outstanding hardness/strength: Microstructural evolution and performance enhancement mechanisms

Incorporation of transition-metal boride with excellent mechanical performance as a reinforcing phase, represents a promising approach to address the challenge of insufficient hardness/strength in Ti6Al4V alloys. Despite the common challenge of achieving homogeneous distribution and refinement of TMB, this study leveraged a novel strategy involving laser-induced in-situ synthesis and a greatly strengthened laser-molten-pool effect, to additively manufacture highly-dense Ti6Al4V-matrix composites reinforced with mono-dispersed TiB nanowires. This was achieved through selective laser melting route of laser powder bed fusion. Remarkably, the unique microstructural morphology of these composites characterized by the uniform dispersion of high-aspect-ratio reinforcing phases, boron dissolution into α-Ti grain boundaries of the Ti6Al4V matrices, and unified crystallographic coordination of gradient transitional layers, contributed to their superior microhardness and compressive strength compared to the counterparts even with the higher contents of reinforcing phases. This achievement was attributed to the synergistic effects of various morphological mechanisms including second-phase, grain refinement, and stress-transfer reinforcing/strengthening. This research provided new insights into the precise control of microstructural evolution in metal-matrix composites and the enhancement of their overall mechanical performance.

Microstructure, phase evolution and mechanical properties of nickel-silicon carbide reinforced Ti6Al4V alloy processed by pulsed electric current sintering

In this work, fully densified Ni–SiC reinforced Ti6Al4V matrix composites were consolidated by pulsed electric current sintering (PECS) technique. The microstructural evolution and mechanical properties of the developed composites with varying SiC contents were investigated. The microstructural study revealed in-situ precipitation of TiC, Ti5Si3 and Ti3SiC2 strengthening phases within the composites. The α colony size in the composites was notably reduced compared to the fabricated SiC-deficient samples due to the addition of SiC additive into the Ti6Al4V alloy matrix. The in-situ precipitated phases enhanced the mechanical properties of the composites. Composite reinforced with 10 wt% SiC (TNi10SiC) displayed the highest hardness value of 609.8 ± 50.9 HV0.5 among the sintered samples, translating to an increment of about 88 % compared to the unreinforced sample T. Among the sintered samples, the highest flexural strength of 2094.32 ± 97.67 MPa was obtained for the TNi5SiC composite, after which the flexural strength deteriorates with increasing SiC content as witnessed in TNi10SiC composite with the least flexural strength of 863.67 ± 71.57 MPa due to agglomeration of the reinforcement phases within the composite. Samples reinforced with 0 wt% SiC experienced a ductile fracture, and the composites containing 2.5 wt% - 5 wt% SiC content witnessed intergranular and interlamellar fractures. However, at higher SiC content, reinforcement pull-out and debonding of the agglomerated reinforcement phases predominates, and composites fail by brittle fracture.

A synergetic effect of ternary refractory nitride reinforcements on densification, mechanical, tribological and thermal stability characteristics of spark plasma sintering-developed Ti6Al4V matrix composites

This paper reports the possibility of developing advanced Ti6Al4V matrix composites (TMCs) with enhanced mechanical properties and highly improved resistance to wear and thermal degradation for structural and high-temperature aerospace applications. The synergetic effect of different weight compositions (1, 1.5 and 2 wt%) of ternary reinforcements consisting of h-BN, TiN and AlN nanoparticles on the characteristics of the microstructure, phase constitution, densification, mechanical, tribological and thermal stability of Ti6Al4V matrix composites developed by spark plasma sintering (SPS) is investigated. The unreinforced Ti6Al4V exhibited a two-phase microstructure made up of α/β phases, however the simultaneous reinforcements resulted in notable microstructural changes and emergence of nitride-rich secondary phases. The relative densities of the composites decrease with increasing reinforcement addition, whereas the nanohardness and elastic modulus values of the composites continue to improve with increasing reinforcement from 1 wt% (28.319 ± 0.525 GPa and 219.43 ± 6.77 GPa) to 2 wt% (55.642 ± 0.693 GPa and 314.59 ± 7.58 GPa) compared to the unreinforced Ti6Al4V (5.838 ± 0.323 GPa and 115.07 ± 3.63 GPa). The unreinforced alloy yields higher average COF values, while the composites at equivalent applied normal loads yield lower average COF values. Thus, in comparison to the unreinforced alloy, the produced composites exhibit considerably lower specific wear rates (with increasing applied normal load). Based on thermogravimetric analysis, the oxidized composite reinforced with 1 wt% of ternary reinforcements exhibits the highest thermal stability in the high-temperature oxidizing environment, as evidenced by its greatest resistance to oxidation and its smallest weight gain of 1.55%.

In situ TiC reinforced Ti6Al4V matrix composites manufactured via selective laser melting

PurposeCurrent methods for the preparation of composite powder feedstock for selective laser melting (SLM) rely on costly nanoparticles or yield inconsistent powder morphology. This study aims to develop a cost-effective Ti6Al4V-carbon feedstock, which preserves the parent Ti6Al4V particle’s flowability, and produces in situ TiC-reinforced Ti6Al4V composites with superior traits.Design/methodology/approachTi6Al4V particles were directly mixed with graphite flakes in a planetary ball mill. This composite powder feedstock was used to manufacture in situ TiC-Ti6Al4V composites using various energy densities. Relative porosity, microstructure and hardness of the composites were evaluated for different SLM processing parameters.FindingsHomogeneously carbon-coated Ti6Al4V particles were produced by direct mixing. After SLM processing, in situ grown 100–500 nm size TiC nanoparticles were distributed within the α-martensite Ti6Al4V matrix. The formation of TiC particles refines the Ti6Al4V β grain size. Relative density varied between 96.4% and 99.5% depending on the processing parameters. Hatch distance, exposure time and point distance were all effective on relative porosity change, whereas only exposure time and point distance were effective on hardness change.Originality/valueThis work introduces a novel, cost-effective powder feedstock preparation method for SLM manufacture of Ti6Al4V-TiC composites. The in situ SLM composites achieved in this study have high relative density values, well-dispersed TiC nanoparticles and increased hardness. In addition, the feedstock preparation method can be readily adapted for various matrix and reinforcement materials in future studies.

Microstructure evolution and mechanical properties of graphene reinforced Ti-6Al-4V matrix composites: Defective vs high-quality graphene

Graphene reinforced Ti6Al4V composites were fabricated by ball milling, fast hot press sintering, and hot rolling. Graphene with two defect states, high quality with pristine structure and low quality with defective structure, was introduced into the Ti6Al4V matrix. The microstructure evolution and mechanical properties of graphene reinforced Ti6Al4V matrix composites were investigated. The results indicated that the high quality graphene/Ti6Al4V composite exhibited good strength-plasticity compatibility while the low quality graphene/Ti6Al4V composite had a severe interface reaction with a wide TiC interlayer and showed poor ductility due to the weak interface bonding.

Nano-SiC whisker-reinforced Ti6Al4V matrix composites manufactured by selective laser melting: Fine equiaxed grain formation mechanism and mechanical properties

Nano-SiC whisker-reinforced Ti6Al4V matrix composites manufactured by selective laser melting: Fine equiaxed grain formation mechanism and mechanical properties

Simultaneous Improvement in Strength and Ductility of TC4 Matrix Composites Reinforced with Ti1400 Alloy and In Situ-Synthesized TiC

To overcome the tradeoff between strength and ductility of materials and obtain titanium matrix composites with excellent mechanical properties, in this study, the in situ-synthesized TiC particles and Ti-Al-V-Mo-Cr (Ti1400) alloy-reinforced Ti6Al4V (TC4) matrix composites ((Ti1400 + TiC)/TC4) were fabricated by low-energy ball milling and spark plasma sintering. The inhomogeneous distribution of TiC particles and Ti1400 alloy, as well as the compositional and structural transition zone, were characterized. The TiC/TC4 composite displayed a significantly higher yield strength and tensile strength compared to the TC4 alloy. However, the total elongation of the TiC/TC4 composite was only 57% of that in the TC4 alloy. In contrast, the (Ti1400 + TiC)/TC4 composites exhibited noticeably higher total elongation than the TiC/TC4 composite. Furthermore, the tensile strength of the composite increased with the increase in Ti1400 alloy content. The increase in strength can be attributed to solid solution strengthening and fine grain strengthening. The compositional and structural transition zone, formed by element diffusion, provided a better interface combination between the reinforcements and TC4 matrix. In the transition zone and Ti1400 region, a large number of α/β interfaces can effectively alleviate the stress concentration, and the increase in the β phase can bear more plastic deformation, which is conducive to improving the elongation of the composite. As a result, the (Ti1400 + TiC)/TC4 composites exhibited simultaneous improvements in strength and ductility.

Realization of synergistic enhancement for strength, wear resistance and ductility via adding La2O3 particles in (TiB+TiC)/Ti6Al4V composite

The hybrid of (TiB + TiC + La2O3) reinforced Ti6Al4V matrix composites (TMCs) were in-situ synthesized by non-consumable arc-melting technology. Effects of addition of La2O3 particles on microstructure evolution, thermal properties, mechanical properties and tribological behavior of the TMCs were investigated. The results indicated that incorporation of La2O3 particles could effectively reduce the average grain size of α-Ti and reinforced phases and increase the ratio of high angle grain boundaries (HAGBs), and grain orientation distribution exhibits more random. The TMCs with addition of La2O3 particles manifests more stable and higher thermal conductivity and lower coefficient of thermal expansion at high temperature. With addition of 0.4 vol% La2O3 particles, TMCs exhibits a near network structure and achieves the good combination of compressive strength (2203 MPa) and ductility (21.45%), which is mainly attributed to particle reinforcement and fine grain strengthening. Compared with TMCs without La2O3 particles, the specific wear rates of TMCs with an increase in La2O3 content from 0.2 vol% to 0.8 vol% reduce by 18.5%, 33.6%, 34.7%, respectively. The wear resistance is enhanced due to synergistic effect of the hetero-deformation induced strain-strengthening and the formation of dense and hard tribo-layer during friction. Significantly, the TMCs with addition of 0.4 vol% La2O3 particles has the best thermal, mechanical and tribological properties. This study may provide a pathway to improve simultaneously the mechanical properties and wear resistance of TMCs for engineering applications.

Microstructure evolution of SiC whisker-reinforced Ti6Al4V matrix composites manufactured by selective laser melting during heat treatment

Ti6Al4V alloy and Ti6Al4V-1SiCw composites were manufactured by selective laser melting (SLM), and the effect of solution aging heat treatment on the microstructure evolution was studied. The experimental results show that the Ti6Al4V alloy after heat treatment had many coarse columnar crystals, forming a strong fiber texture. The microstructure of the composite was uniformly distributed equiaxed grains, resulting in a scattered texture distribution, which greatly reduced the anisotropy of the material properties. After heat treatment, the proportion of low-angle grain boundaries in the composite was larger than that of Ti6Al4V alloy, forming a large number of sub-grain boundaries, thus separating the grains and avoiding the formation of coarse columnar grains. In addition, the heat treatment can effectively reduce the dislocation and internal stress produced in the SLM forming process.

Achieving superior tribological properties of GNPs reinforced Ti6Al4V composites via interface structure design

The severe interface reaction, which has been a challenging problem in graphene nanoplatelets (GNPs) reinforced Ti6Al4V (TC4) matrix composites, results in poor mechanical and tribological properties. Herein, GNPs/TC4 composites exhibited excellent wear resistance by introducing the in-situ TiB whiskers (TiBw) on the interface between GNPs and matrix. This work highlights the mechanical and tribological properties of GNPs/TC4 composites by diminishing the interface reaction and strengthening the interface bonding through the in-situ formed TiBw.

Microstructure and mechanical properties of TiC/Ti6Al4V nanocomposites fabricated by gas–liquid reaction laser powder bed fusion

Herein, we report a novel method for in-situ synthesis of nanometer-scaled TiC-reinforced Ti6Al4V-matrix composites (TMCs) via laser powder bed fusion (LPBF). The formation mechanism can be summarized as in-situ additive manufacturing (AM) via a gas–liquid reaction. Here, gas means the laser-induced pyrolysis methane gas (CH4) generates gaseous carbon (C) atoms/ions and liquid means that the laser beam irradiates Ti6Al4V powder to create a Ti matrix melt pool. TiC, which is the reaction product of gaseous C atom/ion with liquid Ti atom, initially undergoes nucleation and growth, and subsequently precipitates from the Ti matrix melt pool during fast LPBF cooling process. Finally, the TiC-reinforced TMCs are fabricated via a layer-wise gas–liquid reaction. With this method, three nanocomposites (Sample 2, 3 and 7) fabricated in low CH4 concentration (9 vol% and 19 vol%) exhibited good dispersion, clean interface and strong interfacial bonding between the TiC reinforcement and Ti matrix. Thus, it achieved a good combination of simultaneously high strength and high plasticity. The effects of CH4 concentration, laser power and scanning speed on the microstructures and mechanical properties including microhardness, compression behaviors and wear resistance were systematically studied. And the strengthening and toughening mechanisms of the TMCs were elucidated. The proposed in-situ AM method via the gas–liquid reaction would carve a new path for manufacturing uniformly dispersed nano-phase reinforced composites with excellent mechanical properties and complex geometries.

Microstructural characterization and mechanical properties of (TiB + TiC) reinforced Ti–6Al–4V prepared by melt hydrogenation

TiB and TiC reinforced Ti–6Al–4V matrix composites were prepared by melt hydrogenation, in which the total fraction of the reinforcements was 5 vol % and the ratio of TiB to TiC was 1:1. The effects of melt hydrogenation on the solidification process, phase composition, and microstructure of the titanium matrix were studied. The morphology and distribution of the reinforcement without and with hydrogen were observed. Moreover, the nano-hardness of the composites was measured. The results show that the solidification process of the matrix can be changed by melt hydrogenation, which resulting the increase of β phase and refining of α lamellar in titanium alloy. Hydrogen increased the size of the reinforcements, which aggregated at the grain boundary of the primary β phase and formed a network structure. Hydrogen reduced the nano-hardness both of the titanium alloy and the reinforcements slightly. In summary, melt hydrogenation can maintain or slightly reduce the strength of the composites at room temperature and decrease the nano-hardness.

Effects of GNPs on variant selection during quenching of Ti6Al4V matrix composites prepared by hot extrusion

In this work, Ti–6Al–4V matrix composites with GNPs distributed along the extrusion direction(ED) were prepared by hot extrusion, and the effect of GNPs on variant selection of Ti6Al4V alloy during quenching was investigated. The electron backscatter diffraction (EBSD) data showed that GNPs induced variant selection of Ti–6Al–4V, resulting in a difference in the texture intensity distribution of basket-woven α phase in the transverse direction (TD). The contents of various variants in a single grain were analyzed statistics, and the volume changes caused by the variants were calculated. The results show that the interfacial stress of GNPs increases the content of α variants whose volume expansion direction is consistent with the expansion direction of GNPs.

Wire arc additive manufacturing of network microstructure (TiB+TiC)/Ti6Al4V composites using flux-cored wires

Titanium matrix composites (TMCs) with ceramic particles exhibit higher hardness, strength, and wear resistance than those of titanium alloys. Wire arc additive manufacturing (WAAM) is a promising method for fabricating large TMC components owing to its high deposition rate and low production cost. In this study, a WAAM process using a flux-cored wire was developed to fabricate components of TiB plus TiC reinforced Ti6Al4V matrix composites. The network microstructure of the reinforcement was obtained through in-situ reactions induced by the B4C and C powders in the flux core. The formation mechanism of the network microstructure was discussed. The effect of the reinforcement fraction (5 and 10 wt%, hereinafter called 5 and 10 wt% samples) on the microstructure and wear resistance of the samples along the deposition direction were investigated. The results showed that the refined net-basket-dominated (α＋β)-Ti matrix and stable network microstructure were formed in middle region owing to the introduction of the reinforcement. The microhardness increased by 23% and 35% when the reinforcement fractions were 5 and 10 wt%, respectively. The 10 wt% sample showed reduced wear performance because more cracks appeared as the result of the decreased ductility.

Microstructure and mechanical properties of GNPs and in-situ TiB hybrid reinforced Ti–6Al–4V matrix composites with 3D network architecture

Graphene nanoplatelets (GNPs) and TiB whiskers (TiBw) hybrid reinforced Ti–6Al–4V (TC4) matrix composites ((GNPs + TiBw)/TC4) were fabricated by Fast Hot-Press Sintering (FHPS) and hot rolling (HR) method. The microstructure, mechanical properties and strengthening mechanisms were systematically studied with various TiBw contents. Microstructure observation results indicate that GNPs can be mostly preserved and TiBw are rarely obtained during the sintering process. HR process was applied to further densify the composites and obtain the in-situ TiBw. The high ductility of composites was achieved via designing network structure with reinforcements of GNPs and in-situ TiBw, which reduce the interface reaction of the GNPs/Ti and improved the interface bonding. The tensile ductility of the GNPs/TC4 composites were improved with the addition of TiB2 powders. As a result, 0.1 wt% GNPs/TC4 composites with the addition of 0.05 wt% TiB2 powders showed the best combination of ultimate tensile strength of 1158 MPa and a fracture elongation of 15.8%. Compared to the fracture elongation of pure TC4 alloy (15.2%), there was no sacrifice of ductility.

Ti6Al4V/SiC Metal Matrix Composites Additively Manufactured by Direct Laser Deposition

Nowadays, research on additive manufacturing of Ti6Al4V alloy is growing exponentially but there are just a few studies about additive manufacturing of metal matrix composite components. In this work, highly reinforced Ti6Al4V matrix composites with SiC particles have been additively manufactured by direct laser deposition (DLD). Ti6Al4V powder and SiC particles have been deposited layer by layer to form an additive thin wall structure. The geometry, microstructure, and microhardness of the samples are strongly influenced by the laser scanning speed used during de fabrication process. In addition, the effect of the SiC increment in reinforcement concentrations and the influence of SiC particle sizes in the microstructure have been evaluated, and the reaction mechanisms have been established. The percentage of reinforcement measured is lower than expected due to the reinforcement-matrix reactivity that results in partially dissolved SiC particles and the formation of a TiC and Si5Ti3 ring around them. The size and number of particles and reaction products depend on the initial size and percentage of reinforcement and the DLD scanning speed. The higher the size and percentage of SiC particles and reaction products in the matrix, the higher the hardening effect of the composite matrix.Graphic

Ti6Al4V matrix composites fabricated by laser powder bed fusion in dilute nitrogen

In situ synthesised TiN reinforced Ti6Al4V matrix composites were fabricated via laser powder bed fusion (L-PBF) in an atmosphere of 10vol.-% N2 and 90vol.-% Ar based on novel gas–liquid reaction between N2 and Ti6Al4V melt pool. With lower laser energy density (LED), the microstructures of the composites mainly consisted of acicular α′ martensites, while the martensites were shortened and coarsened with increasing LED. The X-ray diffraction analysis demonstrated that the interstitial solid solution of N was formed in the Ti lattice. High-resolution transmission electron microscopy analysis confirmed the generation of TiN. The microhardness, yield strength, ultimate strength and plasticity of the composites initially increased and then decreased with increasing LED. The strengthening mechanisms of the composites were elucidated.

Nanomechanical and Tribological Properties of Hexagonal-Boron Nitride-Enhanced Sintered Titanium Alloy Matrix Composites

This work explored the influence of varied content (1, 3 and 5 wt.%) of hexagonal boron nitride (h-BN) on the nanomechanical and tribological properties of Ti6Al4V matrix composites (TMCs) developed by spark plasma sintering (SPS). Scanning electron microscopy/energy-dispersive X-ray spectroscopy, optical microscopy and X-ray diffraction were employed to characterize the microstructural and phase constituents of the sintered TMCs. Also, nanoindentation and tribology experiment using an automated nanoindenter at maximum load of 200 mN and pin on disk tribometer under 5, 10 and 15 N applied loads were performed, respectively. The results obtained showed that SPS enabled accomplishment of well-refined grains, formation of highly densified product and development of solid matrix-reinforcement interfacial bond. It was also found that the TMCs exhibited continuing enhancement in nanoindentation hardness (50.66 ± 2.25-70.78 ± 3.34 GPa) and modulus of elasticity (238.69 ± 12.25-356.76 ± 21.34 GPa) values and improved tribological properties with increasing h-BN reinforcement content.

Nanosized SiC particle reinforced Ti6Al4V matrix composites manufactured by laser melting deposition

In this work, in-situ (TiC+Ti5Si3)/Ti6Al4V matrix composites (TMCs) with enhanced hardness and wear performance were manufactured by laser melting deposition (LMD) via the addition of nanosized SiC powder. The microstructures of single tracks were investigated to determine the optimal parameters for LMD. Besides, the influence of the SiC content on the microstructural evolutions and mechanical properties was explored. Results demonstrate that the in-situ reaction occurs between SiC and titanium during the LMD process. In-situ TiC and Ti5Si3 were distributed uniformly at grain boundaries and titanium matrix with a full-columnar grains for 0.5 wt.% and 1.0 wt.% SiC addition. The morphology of the composites consists of equiaxed grains with a three-dimensional quasi-continuous network structure when the content of SiC increases to 1.5 wt.% and 3.0 wt.%. The hardness of the composites is 321.1, 342.3, 347.8, and 442.1 Hv with the increasing formation of reinforcements. Meanwhile, the average coefficient of friction decreases from 0.39 to 0.32 with the wear mechanism changing from abrasion to adhesive wear.

In-situ laser additive manufacturing of Ti6Al4V matrix composites by gas–liquid reaction in dilute nitrogen gas atmospheres

Processing titanium (Ti)-based materials in high-concentration nitrogen gas (N2) atmosphere is credited with reducing ductility/plasticity arising from the excessive formation of brittle agglomerated TiN. However processing these materials in dilute N2 may reduce the risk. In this study, a novel method is developed for laser additive manufacturing of in-situ synthesized TiN and AlN co-reinforced Ti6Al4V matrix composites (NTMCs) by the gas–liquid reaction in low-concentration N2 atmospheres. The manufacturing process of the NTMCs involves melting Ti6Al4V powders followed by laser-induced pyrolysis of N2 near the melt pool. The process is facilitated by the reaction between the decomposed nitrogen and molten Ti6Al4V, dissolution and precipitation of nitrides, and formation of the composites layer-by-layer. The formation of the nitride precipitates was verified by XRD, SEM, EDS, and HR-TEM. Such in-situ synthesized nanoscale reinforcements exhibited good dispersion and strong interfacial bonding with the matrix alloy in the composites. The microhardness, 0.2% compressive yield strength, and ultimate compressive strength of the NTMCs significantly increased with increasing N2 concentration in additive manufacturing; their maxima were 511 HV, 1721 MPa, and 2010 MPa, respectively, increased by 36.3%, 67.9%, and 16.8% from those of the Ti6Al4V alloy. The formation and strengthening mechanisms of the NTMCs were elucidated.