Reinforced Titanium Matrix Research Articles

Numerical Study on Mechanical Properties of Discontinuously Reinforced Titanium Matrix Composite with Network Reinforcement Architecture

A two-step finite element modeling method is adopted to predict the elastic properties and reveal the strengthening mechanisms of discontinuously reinforced titanium matrix composites (DRTMCs) with network reinforcement architecture. The microstructure of the composite consists of reinforcement-rich phase (Phase I) and reinforcement-lean phase (Phase II). In the first step, the mechanical properties of Phase I with varying whisker reinforcement content are calculated. In the second step, the calculated mechanical properties are used as input parameters for the homogenized Phase I in the representative volume elements (RVEs) of the composites. In addition, a direct procedure is adopted to generate the exact RVE to validate the two-step method. The predicted elastic moduli obtained by the two-step procedure agree well with those from experiments. Following the same procedure, the strength increase of the composites contributed by the two mechanisms, i.e., load-transfer by the reinforcement and matrix strengthening caused by grain refinement, solution strengthening, etc., can be determined from the simulations separately, which shows that the strength enhancement of the DRTMCs with the addition of TiB whiskers by in situ reaction is primarily due to the matrix strengthening rather than the load-transfer mechanism.

Comparison of Residual Stress Measured by Diffraction Method and Matrix Etching Method in SiC Fiber Reinforced Titanium Matrix Composites

Measurement and modeling of residual stresses in SiC fiber reinforced titanium matrix composites (SiCf/Ti) are still a challenge. Diffraction method and matrix etching method can characterize the strains of matrix and fiber, respectively. A In this work, SiCf/Ti samples with perpendicular and parallel cross-sections to the fibers have been fabricated, and the residual stresses were measured by X-ray diffraction and matrix etching. The results showed that the axial matrix stress in sample with perpendicular cross-sections to the fibers was larger than that in sample with parallel cross-sections to the fibers, while the axial matrix stress calculated from etching was consistent with that from X-ray diffractions based on triaxle stress model, confirming the reliability of triaxle stress model.

The effect of severe plastic deformation on the microstructure and mechanical properties of (TiB+TiC) reinforced titanium matrix composites

Equal-channel angular pressing (ECAP) was successfully applied to in-situ synthesized particulate reinforced titanium matrix composites. The results prove that the ultrafine-grained structure can be effectively obtained in the titanium matrix composite by ECAP at different temperatures and passes. Formation of homogenous TiB and TiC particles with ultrafine grains and sub-grains were obtained after 4 ECAP passes, which indicates that the reinforcement-induced ultrafine grains. The lamellar α phases are also twisted obviously due to the shear stress, which can reduce the average thickness of lamellar α phases to less than 1μm. After ECAP at relatively low temperature, dislocation pile-ups, dislocation tangling and plenty of cell structures with size of about 500nm can be observed in the matrix. While many newly formed ultrafine grains with clear grain boundaries and size of 100~500 nanometers have formed. The tensile test results show that the yield strength is improved by ECAP pressing and saturate after 4 ECAP passes to a value of 1150MPa, and the ductility is much higher compared with the first ECAP pass.

Effect of TiB2 content on the characteristics of spark plasma sintered Ti–TiBw composites

Spark plasma sintering (SPS) was employed to fabricate monolithic titanium and in-situ formed TiB whisker (TiBw) reinforced titanium matrix composites (TMCs) by adding different amounts of TiB2 as boron source. The sintering process was completed at 1050°C for 5min under 50MPa. The influences of TiB2 content (0.6–9.6wt. %) on microstructural evolution and mechanical properties of TMCs were investigated. Thermodynamics, XRD analysis and microstructural investigations confirmed the in-situ formation of TiBw in the composite samples. However, some semi-reacted TiB2 phases, surrounded by TiB coronas, were remained in the microstructure due to the unfinished chemical reaction between the components during a short-time sintering process. The results showed that all samples were appropriately densified by SPS process into the almost dense parts with relative density no less than 97.5%. While bending strength decreased and hardness increased with increasing TiB2 content, the sample with 4.8wt. % TiB2 had the maximum tensile strength. Fractographical assessments showed that the addition of TiB2 hindered the grain growth of titanium matrix. With increasing TiB2 content, fracture mode changed from a multiple pattern to a predominantly transgranular and brittle state.

In-situ ultrafine three-dimensional quasi-continuous network microstructural TiB reinforced titanium matrix composites fabrication using laser engineered net shaping

In this study, we created an innovative ultrafine three-dimensional quasi-continuous network (3DQCN) microstructure by in-situ laser engineered net shaping (LENS) of TiB reinforced titanium matrix composites (TiB-TMCs). As a rapid solidification process, the LENS process enabled high degree of Ti grain refinement. The in-situ processed eutectic TiB aggregated at these Ti grain boundaries, forming the ultrafine 3DQCN microstructure. The microstructural characterizations of the ultrafine 3DQCN microstructure were investigated. Effects of the TiB reinforcement and the ultrafine 3DQCN microstructure on the mechanical performance of the fabricated parts were studied. The results demonstrated that the TiB-TMCs with the ultrafine 3DQCN microstructure exhibited superior mechanical properties.

Microstructure and mechanical properties of carbon nanotubes reinforced titanium matrix composites fabricated via spark plasma sintering

The influence of various dispersion methods on the evolution of multi-walled carbon nanotubes (MWCNTs) in titanium (Ti) metal matrix composites (TMCs) prepared via spark plasma sintering (SPS) have been investigated. The synthesis procedures included sonication, high energy ball milling (HEBM), and rapid consolidation of powder mixtures at different sintering temperatures. The impact energy provided to the powder mixtures during HEBM process was optimized to disperse 0.5wt% MWCNTs into Ti matrix in two controlled ball milling processes: with and without in-situ formation of TiC during HEBM. The interfacial reactions between MWCNTs and Ti matrix were controlled by retaining the crystallinity and sp2 carbon network of the MWCNTs even at high sintering temperature of 800°C, which enhanced their compressive strength up to 1056MPa with a compressive strain of 27.31%. The mechanical and tribological properties of the composites consolidated from the powder mixtures with in-situ TiC formation during HEBM and pre-sonicated MWCNTs were significantly enhanced as opposed to the composites consolidated from the powder mixtures without formation of TiC during HEBM.

Microstructure and mechanical properties variation of TiB/Ti matrix composite by thermo-mechanical processing in beta phase field

TiB reinforced titanium matrix composite with a near alpha alloy matrix was fabricated using in situ technologies. The Widmanstatten microstructure evolution of the composite and the TiB whiskers realignment effect during thermo-mechanical processing were investigated, and the mechanical properties of the composite were measured. It was found that the microstructure of the composite is refined significantly by the thermo-mechanical processing due to the recrystallization of beta grains. With the increase in deformation amplitude, the value of probability density of small orientation angles of TiB whiskers along extension direction increases sharply. Strength of the composite was increased significantly by the thermo-mechanical processing, which results from the increase in the strengthening effect of TiB whisker and the microstructure refinement. The value of the thickness of alpha plates (b) without precipitated sillicide has minor effect on the strength of the composite but it becomes a non-ignorable strengthening factor after sillicide precipitation due to its dislocation hindering effect.

The mechanical behavior dependence on the TiB whisker realignment during hot-working in titanium matrix composites

Low-cost TiB whiskers reinforced titanium matrix composite (TMCs) was fabricated with enhanced mechanical performances using in situ technologies and hot working. Morphologies observation indicates that needle-like TiB whiskers with a hexagonal transverse section grow along the [010] direction due to B27 crystal structure and its growth mechanism. Mechanical properties tests show that the mechanical behavior of the TiB whiskers reinforced TMCs is dependent on the deformation amplitudes applied in hot-working. The improvement in yield strength by hot-working is attributed to the TiB whiskers realignment and the refinement of microstructure. Models are constructed to evaluate the realignment of TiB whisker during deformation and the increase in yield strength of the composite at elevated temperatures. These models clarify the alignment effect of TiB whiskers under various deformation amplitudes applied in hot-workings and reveals the yield strength dependence on TiB whiskers orientation.

Prediction of grinding temperature of PTMCs based on the varied coefficients of friction in conventional-speed and high-speed surface grinding

In this article, the finite element model containing the varied coefficients of friction is established in order to improve the prediction accuracy of surface grinding temperature of particulate reinforced titanium matrix composites (PTMCs). The coefficients of friction, such as 0.46 for conventional-speed grinding and 0.21 for high-speed grinding, respectively, are determined according to the grinding forces ratios measured. Results obtained show that the relative error of experimental and predicted grinding forces is limited within 2∼9 %, while the relative error of experimental and predicted grinding temperatures values is controlled at 7∼15 %. The prediction accuracy is improved significantly based on the varied coefficients of friction in surface grinding of PTMCs.

High speed grinding of particulate reinforced titanium matrix composites using a monolayer brazed cubic boron nitride wheel

This paper aims at investigating the machinability of particulate reinforced titanium matrix composites (PTMCs) during high speed grinding (80–140 m/s) using a monolayer brazed cubic boron nitride (CBN) superabrasive wheel. The removal mechanism of the hard-brittle reinforcements of PTMCs is discussed based on finite element simulation. Results obtained show that the grinding forces, temperature, specific energy, and ground surface roughness of PTMCs were usually higher than those of Ti-6Al-4V alloy under the defined experimental conditions. The undeformed chip thickness has a great effect on the removal behavior of the hard-brittle reinforcements of PTMCs, which can result in different defects in the ground surface. Finally, the microstructure alteration and hardening phenomenon in the subsurface layer were characterized quantitatively.

A MIM Route for Producing Ti6Al4V-TiC Composites

Discontinuous reinforced titanium matrix composites have generated significant interest due to their compelling properties such as their specific strength and wear resistance at room and elevated temperatures. For these reasons, these materials have been considered in various applications such as automotive (valve components), aerospace (engine components) and medical devices (implants). Metal injection molding (MIM) has proven to be an efficient near net-shape technology suitable for high volume manufacturing of parts having complex geometries. The MIM technology is particularly attractive for producing composites as the metallic matrix does not go through the liquid state. This helps minimizing the segregation of the hard particles. MIM also reduces the needs for machining. However, the production of titanium components with the MIM process has its own challenges and limitations, such as presence of porosities and coarser microstructures compared to wrought products. The present work introduces the results obtained during the development of a MIM route for producing Ti6Al4V-5wt%TiC composites. The feedstock developed is wax-based and incorporates a pre-alloyed metal powder. The microstructure, mechanical properties at room and elevated temperatures, the wear resistance and the thermal diffusivity of the composites have been characterised. Properties are compared with those of a Ti6Al4V MIM material produced with the same feedstock and process but without TiC as well as with those of wrought Ti6Al4V reported in the literature. The presence of a small amount of TiC promotes densification and grain size refinement and affects the surface finish of the sintered components. Tensile properties of the composites are comparable or better than those of wrought Ti6Al4V (ASTM F1472). Improved mechanical properties compared to unreinforced material are associated to the higher density, finer grain size as well as solution strengthening of the titanium matrix.

Numerical Simulation on Residual Stress of SiC Fiber Reinforced Titanium Matrix Composite

Numerical Simulation on Residual Stress of SiC Fiber Reinforced Titanium Matrix Composite

Microstructure and properties of TiB2–TiB reinforced titanium matrix composite coating by laser cladding

TiB2 particle and TiB short fiber reinforced titanium matrix composite coatings were prepared utilizing in situ synthesized technique by laser cladding on the surface of Ti6Al4V alloy. Through the experiment, it was found that the surface of the single-track coatings appeared in the depression, but it can be improved by laser track overlapping. With the increase of laser power density, the amount of TiB short fiber was increased, and the distribution of TiB2 and TiB became more uniform from the top to bottom. The micro-hardness of TiB2/TiB coating showed a gradient decreasing trend, and the average micro-hardness of the coatings was two-fold higher than that of the substrate. Due to the strengthening effect of TiB2 particle and TiB short fiber, the wear volume loss of the center of the coating was approximately 30% less than that of the Ti–6Al–4V substrate, and the wear mechanism of the coating was mild fatigue particle detachment.

Effect of Zr, Mo and TiC on microstructure and high-temperature tensile strength of cast titanium matrix composites

In this paper, five types of TiC particle reinforced titanium matrix composites (TiC-PTMCs) were fabricated by casting route in order to investigate the influence of Zr, Mo and TiC on microstructures and tensile strengths of TiC-PTMCs. The increase of Zr content promoted the precipitation of eutectic TiC and refined primary TiC, while increasing Mo content led to the refinement of α lath. The composites with high Zr and Mo contents and low TiC content showed superiority in ultimate tensile strength (UTS) below 650°C, whereas above 700°C, high UTS was obtained in the composites with high TiC content and low Mo content. Below 650°C, solid solution strengthening and fine grain strengthening of matrix make the largest contribution to the improvement of UTS. However, above 700°C, solid-solution strengthening of Zr and the load bearing effect of TiC play a dominant role in the enhancement of UTS. Accordingly, effective routes for improving UTSs of TiC-PTMCs in different temperature ranges are different.

Tribological, electrochemical and in vitro biocompatibility properties of SiC reinforced composite coatings

In this work, laser engineered net shaping (LENS™) technique was used to create SiC reinforced titanium matrix composite (TMC) on titanium surface. These composite coatings developed by injecting SiC powder into titanium melt pool, created using a high-power laser. The laser parameters strongly influenced the dissolution of SiC particles leading to formation of TiSi2, Ti5Si3, and TiC phases along with residual SiC in the composite layers. A graded microstructure, with high concentration of secondary phases on top compared to the bottom region was formed. The reinforcing ceramic phases in the TMC coatings enhanced the wear resistance of titanium by about 100 times. The wear resistance of the composite coatings in physiological environment found to increase with increase in the laser power and concentration of SiC particles injected into the melt pool. These composite coatings also showed better corrosion resistance than Ti. In vitro biocompatibility studies performed using osteoblast (MG63) and fibroblast cells (NIH3T3) demonstrated non-toxic nature of these composite coatings. It is envisioned that such coatings may find applications in articulating surfaces of load-bearing implants to enhance their in vivo lifetime with reduced metal ion release.

Comparative investigation on high-speed grinding of TiCp/Ti–6Al–4V particulate reinforced titanium matrix composites with single-layer electroplated and brazed CBN wheels

In order to develop the high-efficiency and precision machining technique of TiCp/Ti–6Al–4V particulate reinforced titanium matrix composites (PTMCs), high-speed grinding experiments were conducted using the single-layer electroplated cubic boron nitride (CBN) wheel and brazed CBN wheel, respectively. The comparative grinding performance was studied in terms of grinding force, grinding temperature, grinding-induced surface features and defects. The results display that the grinding forces and grinding temperature obtained with the brazed CBN wheel are always lower than those with the electroplated CBN wheel. Though the voids and microcracks are the dominant grinding-induced surface defects, the brazed CBN wheel produces less surface defects compared to the electroplated wheel according to the statistical analysis results. The maximum materials removal rate with the brazed CBN wheel is much higher than that with the electroplated one. All above indicate that the single-layer brazed CBN super-abrasive wheel is more suitable for high-speed grinding of PTMCs than the electroplated counterpart.

Characteristics of Ti(C, N)/TiB composite layer on Ti–6Al–4V alloy produced by laser surface melting

A Ti(C, N)/TiB reinforced titanium matrix composite layer was successfully in-situ synthesized by laser melting on Ti–6Al–4V alloy surface with Ti–BN–C mixed powder, aiming at improving the wear resistance. The microstructure, chemical composition, hardness and wear behavior were analyzed. The results showed that, the cross sectional microstructure can be clearly divided into three parts, which were the laser melted layer, heat affected zone and non-affected zone. The reinforcements in laser melted layer consisted of dendritic TiC0.3N0.7 phases and fine-structure TiB phases. The matrix in laser melted layer was in a two-phase structure, being composed of platelet α titanium and intergranular β titanium. The hardness was increased from 320 HV in the substrate to 450–550 HV in the modified layer. The wear resistance was improved that, the wear volume loss of the laser treated sample was approximately half of the as received Ti–6Al–4V alloy after 8h wear test.

Fabrication and characterisation of Titanium Matrix Composites obtained using a combination of Self propagating High temperature Synthesis and Spark Plasma Sintering

This work presents a novel processing method for the fabrication of particle reinforced Titanium Matrix Composites (TMCs). TMCs are a promising alternative to improve the mechanical properties of titanium alloys. In the processing method, the reinforcement (TiC–Ti) was obtained by Self-propagating High-temperature Synthesis (SHS). The composition of the reinforcement was Ti1.3C. An excess of titanium compared to the equiatomic TiC was introduced in the reaction in order to control the size of the reinforcement and to improve the compatibility between reinforcement and matrix. This reinforcement was mixed with Ti–6Al–4V powder and the final consolidation of the TMC was performed by Spark Plasma Sintering (SPS). The microstructure and mechanical characterisation of the TMCs are presented. Comparing tensile properties with conventional Ti–6Al–4V alloys, the materials developed in this work present higher young modulus and tensile strength. In addition, in order to study the possible scale up of SPS process for the production of TMCs, the manufacturing of large samples was studied.

Dynamic Constitutive Model for TiC-Particulate Reinforced Titanium Matrix Composites

A coupled model of damage and plasticity is presented to describe the dynamic behaviors of TiC-particulate reinforced titanium matrix composites (TiCp/TMCs) subjected to shock loadings. The TiCp/TMCs are assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to TiCp/TMCs is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, the smashing destroy takes place. The model parameters for TiCp/TMCs are determined using plate impact experiments. Comparison with the test results shows that the proposed model can give consistent predictions of the dynamic behaviors of TiCp/TMCs subjected to impact loadings.

Rapid and low temperature spark plasma sintering synthesis of novel carbon nanotube reinforced titanium matrix composites

Multi–walled carbon nanotube (MWCNT) reinforced titanium matrix composites were synthesized using a spark plasma sintering method at a low sintering temperature of 550 °C. The effects of the weight fraction of MWCNTs on the microstructures and the mechanical and thermal properties of the composites were investigated. No reaction products were detected in the composites, indicating that the MWCNTs in the composites maintained their structural integrity after sintering, and thus, because of their advantageous properties, could reinforce the titanium matrix. As a result, the compressive strength of the composite containing 0.4 wt.% MWCNTs reached 1106 MPa, which was an increase of 61.5% compared to that of pure titanium under at the same conditions. In addition, the results revealed that compressive strength of the bulk compacts increased initially and then decreased with an increase in weight fraction of MWCNTs. However, compressive strain of the sintered composites continued to fall at a slow rate. The microhardness and thermal diffusivity of the composites rose steadily with an increasing content of MWCNTs. When the weight fraction of MWCNTs in the composites exceeded 0.8%, the compressive strength of the composites declined significantly due to the increasing aggregation of the MWCNTs.