Blended Elemental Powder Metallurgy Research Articles

Unveiling the impact of heat treatment on powder-metallurgy α+β titanium alloy for achieving a superior strength-ductility combination

The present study investigated the effects of heat treatment (solid solution and aging treatments) on the microstructure and mechanical properties of a hot-rolled α+β Ti–3Al–5Mo–4.5V (TC16) produced through blended elemental powder metallurgy (BEPM) process using master alloy hydrogenation (MAH) approach. After solid solution treatment, metastable martensite α'' phase and athermal ω phase were formed. Aging treatment facilitated decomposition of metastable phases and precipitation of αs particles. Dispersion strengthening, resulting from the formation of a significant amount of α/β interfaces between fine secondary αs particles and β matrix, played a decisive role in enhancing the strength of the TC16 alloy. However, elevated aging temperatures promoted the coarsening of αs particles, leading to a reduction in the strengthening effect. A systematic investigation of the effects of the solid solution and aging treatments enabled the evolution of a bimodal microstructure with the precipitation of fine αs particles, contributing to an outstanding combination of strength and ductility. The ultimate tensile strength reached 1424.6 MPa with an elongation at break of 7.7%, while the hardness reached 380.2HV.

Ballistic performance of titanium-based layered composites made using blended elemental powder metallurgy and hot isostatic pressing

Metal matrix composites tiles based on Ti–6Al–4V (Ti64) alloy, reinforced with 10, 20, and 40 (vol%) of either TiC or TiB particles were made using press-and-sinter blended elemental powder metallurgy (BEPM) and then bonded together into 3-layer laminated plates using hot isostatic pressing (HIP). The laminates were ballistically tested and demonstrated superior performance. The microstructure and properties of the laminates were analyzed to determine the effect of the BEPM and HIP processing on the ballistic properties of the layered plates. The effect of porosity in sintered composites on further diffusion bonding of the plates during HIP is analyzed to understand the bonding features at the interfaces between different adjacent layers in the laminate. Exceptional ballistic performance of fabricated structures was explained by a significant reduction in the residual porosity of the BEPM products by their additional processing using HIP, which provides an unprecedented increase in the hardness of the layered composites. It is argued that the combination of the used two technologies, BEPM and HIP is principally complimentary for the materials in question with the abilities to solve the essential problems of each used individually.

A Comprehensive Study on Hot Deformation Behavior of the Metastable β Titanium Alloy Prepared by Blended Elemental Powder Metallurgy Approach

A Comprehensive Study on Hot Deformation Behavior of the Metastable β Titanium Alloy Prepared by Blended Elemental Powder Metallurgy Approach

Significant hardening effect of high-temperature aging of alloy Ti-6Al-4V composite reinforced with TiC

Titanium alloy composites, reinforced with a light second phase and made using inexpensive powder metallurgy, attract considerable attention due to the directness of their intentional hardness increase without compromising low weight of materials. In this study the metal-matrix composites (MMC) of Ti-6Al-4V alloy reinforced with light and hard particles of TiC (up to 80%, vol.) were made using blended elemental powder metallurgy of hydrogenated titanium. Post-sintering solution treatment for 45 min. at 880 °C and 1000 °C and water quenching followed by the 5 hrs. aging at 550 °C was used to additionally refine the microstructure and properties of MMC. For the duration of thermal exposure throughout solution treatment and additional aging the matrix and reinforcement phase underwent distinct structural changes that modified the mechanical properties of materials. It has been shown that the used reinforcement presents an exceptional opportunity for hardening of Ti-based composites without compromising their low specific weigh. It can increase the hardness of material by more than 40% due to the ability of TiC to chemically react with the matrix to form a strong interfacial bond and its ability to form hard compounds of Ti2C and Ti3AlC in the expense of the relatively soft matrix alloy.

An Investigation into the Microstructural Response to Flexural Stresses of a Metastable β‐Phase Ti Alloy produced by Blended Elemental Powder Metallurgy

A Ti‐10V‐3Al‐3Fe metastable β Ti alloy is strained under three‐point bending conditions according to the ASTM E290‐14 standard. A combination of electron backscatter diffraction (EBSD) mapping and high‐resolution scanning transmission electron microscopy (STEM) is used to investigate the microstructural response to flexural stress. Results reveal a delayed formation of the deformation products, due to the load‐bearing capacity of the constituent voids. The deformation products are confined in narrow bands on either side of the fracture surface. {332}⟨113⟩ twinning system is identified as the primary deformation mode followed by the formation of α″ martensite both in β matrix and β twins. Accommodation of the microscopic strain arising from the development of α″ structure and β‐twinning triggers the formation of fine deformation‐induced ω plates, which are observed predominantly at the interfacial plane of β/β twin and β/α″, and also in the interior of the β twins.

In-situ synthesized TiC/Ti-6Al-4V composites by elemental powder mixing and spark plasma sintering: Microstructural evolution and mechanical properties

Titanium matrix composites synthesized using powder metallurgy methods have attracted significant attention due to their extraordinary mechanical properties. In this study, cost-effective and high-performance TiC/Ti-6Al-4 V matrix composites were synthesized and characterized using a combined elemental powder mixing and spark plasma sintering method. Studies on the effect of graphene nanoplate (GNP) content on microstructures of Ti-6Al-4 V matrix composites showed typical Widmanstatten structures without apparent pores and microcracks. The grain size of composites was decreased significantly with the increase of GNP content, mainly due to the pinning effect of in-situ generated TiC particles at grain boundaries, which limited the rapid grain growth of the matrix. Mechanical test results showed that their yield strength and ultimate tensile strength were 889.0 MPa and 988.3 MPa, respectively, and their total fracture elongation was maintained at ∼14.2 %. GNPs/Ti-6Al-4 V exhibited superior strength (e.g., yield and ultimate tensile strength of 1028.4 and 1121.6 MPa, which are 14.4 % and 13.5 % higher than those of the matrix) and maintained a good ductility of ∼ 9.8 % with only 0.1 wt% GNP addition. Carbon nanomaterial (such as graphene nanoplates) induced the precipitation of needle-like nano-secondary phases in trigeminal grain boundary β phases, which strengthened the β-Ti soft phase. The reinforced strength of the composite is mainly attributed to the grain refinement, secondary α phases precipitation strength and dislocations strengthening. This work provides a new methodology for fabrication of high-performance titanium matrix composites (TMCs) combination blended elemental powder metallurgy (BEPM) and sintering technology.

Microstructural Characteristics of Ti‐Based Composites with Various Ceramic Reinforcements Manufactured via Hydrogen‐Assisted Blended Elemental Powder Metallurgy

Highly dense in situ reinforced titanium matrix composites are fabricated with hydrogen assisted two-stage press-and-sintering method as described in the article, number 2101689 by Yuchao Song, Tuo Cheng, Orest Ivasishin and co-workers. Type and size of starting ceramic additives have substantial impact on the microstructure formation, residual porosity, and hardness of the pre-sintered composites. Sintering of hydrogenated pre-alloyed powders at second processing stage ensures desirable microstructure, improved density and uniformity of composites.

A novel method to fabricate high strength and ductility Ti-3Al-5Mo-4.5 V alloy based on TiH2 and pre-hydrogenated master alloy powders

Fabrication of high-performance titanium (Ti) alloys containing high-melting-point elements is challenging via blended elemental powder metallurgy (BEPM), because of the inevitable high porosity induced during pressing and sintering processes. Herein, we propose a novel master-alloy pre-hydrogenation (MAPH) method to fabricate sintered TC16 (Ti-3Al-5Mo-4.5 V) alloy, which possess a nearly full-density (99.2%) and good mechanical properties, i.e., an UTS of ∼ 1004.6 MPa, a YS of ∼934.2 MPa and an EL of ∼15.8%. The pre-hydrogenated 7.5Ti-3Al-5Mo-4.5V-Hx (7.5TiMA-Hx) powder particles show a morphology of sharp corners. Therefore, the 7.5TiMA-Hx and TiH2 particles can get interlocked compactly during compaction and shrink simultaneously during the dehydrogenation process, which minimizes the difference in volume mismatch and ensures the overall uniformity after sintering. Besides, the interlocking compact structure makes the element diffusion easier between the 7.5TiMA-Hx and TiH2 matrix particles, which promotes the healing of porosity. The low porosity can reduce the tendency for propagation of cracks along the grain boundaries of the α layer, leading to a good balance between the strength and ductility of the sintered TC16-7.5TiMA-Hx alloy.

Mechanical behavior of bilayer structures of Ti64 alloy and its composites with TiC or TiB under quasi-static and dynamic compression

Bilayer structures of titanium alloy Ti-6Al-4V (Ti64) and metal matrix composites (MMC) on the base of this alloy reinforced with 5, and 10 % (vol.) of TiC or TiB particles were made using press-and-sinter Blended Elemental Powder Metallurgy (BEPM). The mechanical behavior of these structures was studied under quasi-static and high strain rate compression. Dynamic tests with compression velocity in the range 4–15 m/s (820–2880 s−1) were done using the split Hopkinson pressure bar (SHPB), whereas the quasi-static tests were performed with compression velocity of 0.0005 m/s (10−3 s−1). Stress–strain curves were obtained and the effect of phase composition, microstructure, and strain rate was analyzed and discussed. Current results were compared with previous studies conducted on homogeneous MMCs and Ti64 alloy tested in similar conditions. The deformation mechanism evaluated from the microstructure analysis of the samples was verified using in-situ high-speed camera recordings. Numerical simulation based on Finite Element Analysis was conducted to further investigate the behavior of the samples during the SHPB trials. Generalized scheme of the deformation and damage process of two-layer alloy/composites hybrids as a function of compression rate was proposed.

Microstructural Characteristics of Ti‐Based Composites with Various Ceramic Reinforcements Manufactured via Hydrogen‐Assisted Blended Elemental Powder Metallurgy

The manufacturing of in situ reinforced titanium matrix composites by the sintering of titanium hydride and ceramic powder blends is an attractive and cost‐efficient process. Herein, a novel two‐stage (double‐compaction/double‐sintering) hydrogen‐assisted powder approach is suggested to produce uniform highly dense Ti‐based composites reinforced with TiB, TiC, and dual TiC + TiB phase particles. In this approach, the hydrogenation and milling of presintered products enable the initial porous materials to transform into hydrogenated prealloyed (PA) powders of controlled sizes, and a second press‐and‐sinter process further converts the PA powders into nearly dense composite microstructures with evenly distributed fine reinforcements. The adverse effect of the raw reinforcing powder size on microstructure uniformity, porosity, and mechanical characteristics of the presintered in situ composites becomes negligible in final sintering stage. The reduction of the porosity and enhancement of the hardness indicate that the hydrogen‐assisted double‐compaction and double‐sintering blended elemental powder metallurgy (BEPM) + PA approach enables the low‐cost fabrication of Ti‐based composites with suitable mechanical characteristics.

Manufacturing of biomedical Ti alloys with controlled oxygen content by blended elemental powder metallurgy

Biomedical Ti-xNb-7Zr-0.7O (wt%) alloys were manufactured from elemental powders and controlled addition of TiO2 using field assisted sintering technique (FAST). First, sintering parameters were optimized on the benchmark Ti-29Nb-7Zr-0.7O alloy. Second, alloys with various content of Nb (20, 23, 26 and 29 wt%) were manufactured. FAST is capable to produce homogeneous material with controlled amount of oxygen. In addition, FAST is a valuable method for fast sampling of alloys with different compositions. Detailed XRD and SEM study proved that oxygen prevents formation of α” martensite phase. Presence of α phase, α” phase and especially ω phase causes an increase of elastic modulus and microhardness. Single phase β Ti-29Nb-7Zr-0.7O alloy can be manufactured by FAST from elemental powders and subsequent solution treatment. The alloy is proposed for biomedical use due to its low elastic modulus.

In Situ Ti6Al4V/TiB Composites Prepared by Hydrogen-Assisted Sintering of Blends Containing TiH2 and Ball-Milled Ti+TiB2 Powders.

In the present study, 98.6–99.5% dense in situ reinforced Ti6Al4V/TiB composites were manufactured with a newly developed approach based on hydrogen-assisted blended elemental powder metallurgy (BEPM). The approach includes the activation milling of titanium powder produced with hydrogenation-dehydrogenation (HDH-Ti powder) with finer TiB2 additives, following blending with TiH2 and master alloy (MA) powders, and final press-and-sinter operations. Scanning electron microscope (SEM) observations prove the formation of microstructures with improved density and homogeneous distribution of TiB reinforcements in a sintered Ti6Al4V matrix. Hardness and compressive tests validated the high mechanical characteristics of produced composites. The effect of preliminary milling time over 2–6 h and the ratio of hydrogenated and non-hydrogenated titanium powders used (TiH2 vs. HDH Ti) on microstructure and mechanical properties were studied to further optimize the processing parameters. Test results indicate the above approach can be regarded as a promising route for the cost-effective manufacturing of Ti6Al4V/TiB composite with reduced porosity, tailored microstructure uniformity, acceptable impurity level and, hence, mechanical characteristics sufficient for practice applications.

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.

Mechanical Behavior of Titanium Based Metal Matrix Composites Reinforced with TiC or TiB Particles under Quasi-Static and High Strain-Rate Compression.

The mechanical behavior of titanium alloys has been mostly studied in quasi-static conditions when the strain rate does not exceed 10 s−1, while the studies performed in dynamic settings specifically for Ti-based composites are limited. Such data are critical to prevent the “strength margin” approach, which is used to assure the part performance under dynamic conditions in the absence of relevant data. The purpose of this study was to obtain data on the mechanical behavior of Ti-based composites under dynamic condition. The Metal Matrix Composites (MMC) on the base of the alloy Ti-6Al-4V (wt.%) were made using Blended Elemental Powder Metallurgy with different amounts of reinforcing particles: 5, 10, and 20% of TiC or 5, 10% (vol.) of TiB. Composites were studied at high strain rate compression ~1–3·103·s−1 using the split Hopkinson pressure bar. Mechanical behavior was analyzed considering strain rate, phase composition, microstructure, and strain energy (SE). It is shown that for the strain rates up to 1920 s−1, the strength and SE of MMC with 5% TiC are substantially higher compared to particles free alloy. The particles TiC localize the plastic deformation at the micro level, and fracturing occurs mainly by crushing particles and their aggregates. TiB MMCs have a finer grain structure and different mechanical behavior. MMC with 5 and 10% TiB do not break down at strain rates up to almost 3000 s−1; and 10% MMC surpasses other materials in the SE at strain rates exceeding 2200 s−1. The deformation mechanism of MMCs was evaluated.

Optimization of processing parameters to produce nearly dense fine-grained Ti–6Al–4V microstructures with a hydrogen-assisted BEPM approach

Abstract In the present study, fine-grained and nearly dense Ti–6Al–4V alloy is produced by press-and-sinter blended elemental powder metallurgy using titanium hydride powder. Methods to produce a desirable alloy microstructure at a relatively low ( 1100 °C ) sintering temperature are developed, including thermocycling around the α ↔ β transus temperature and hydrogenation–dehydrogenation of powder compacts at 850 °C to realize the alpha-beta phase transformations. The associated volume changes promote acceleration of diffusion and enhanced densification. A sintering regime combining these two treatments incorporates their respective advantages of retarded grain growth and improved densification during sintering at 1100 °C . The fine grain size (~45 μm), acceptable oxygen content (0.17%–0.21%), and reduced residual porosity (~2%) of the as-sintered Ti–6Al–4V provide tensile characteristics (880 ± 20Mpa of UTS, 15 ± 2% of Elongation) suitable for practical application.

Predicting Workability of a Low-Cost Powder Metallurgical Ti-5Al-2Fe-3Mo Alloy Using Constitutive Modeling and Processing Map.

A low-cost titanium alloy (Ti–5Al–2Fe–3Mo wt.%) was designed and fabricated by blended elemental powder metallurgy (BEPM) process. The high-temperature deformation behavior of the powder metallurgical Ti–5Al–2Fe–3Mo wt.% (PM-TiAlFeMo) alloy was investigated by hot compression tests at temperatures ranging from 700 to 1000 °C and strain rates ranging from 0.001 to 10 s−1. The flow curves were employed to develop the Arrhenius-type constitutive model in consideration of effects of deformation temperature, strain rate, and flow stress. The value of activation energy (Q) was determined as 413.25 kJ/mol. In order to describe the workability and predict the optimum hot processing parameters of the PM-TiAlFeMo alloy, the processing map has been established based on the true stress–true strain curves and power dissipation efficiency map. Moreover, microstructure observations match well with the analyses about deformation mechanisms, revealing that dynamic recovery and dynamic recrystallization are dominant softening mechanisms at relatively high temperatures. However, the kinking and breaking of microstructure prefer to occur at relatively low temperatures.

Central Composite Experiment Design (CCD)-Response Surface Method (RSM) to Optimize the Sintering Process of Ti-6Al-4V Alloy

It is widely acknowledged that the blended elemental (BE) powder metallurgy (PM) Ti6Al4V alloy attracted unusual due to its low cost and comprehensive mechanical properties. However, the high porosity and mediocre mechanical properties of traditional vacuum sintering limited its application. To achieve better mechanical performance, the central composite designs (CCDs) method was employed to analyze the influence of sintering parameters, such as sintering temperature (St), heating rate (Hr), and holding time (Ht). The results indicated that St makes the most significant contribution to compressive strength and sintering density, accounting for 95.5% and 86.54% respectively. In addition, Ht makes the most significant contribution to compression ratio, which accounted for 89.35%. Through the analysis of response surface methodology (RSM), the optimum sintering parameters (St, Ht, Hr) could be considered to be 1300 °C, 148 min and 5 °C/min. In addition, verification experiments were carried out under the optimum conditions, and the experimental results were in good agreement with the predicted values, since the deviation of the predicted and experimental values was less than 4.9%. Therefore, the results of this study could certify the reliability of CCDs method, which would contribute to the development of titanium alloys with low cost and high mechanical properties.

Effect of strain on microstructural development during uniaxial compression of metastable beta Ti–10V–2Fe–3Al alloy

The effect of strain during uniaxial compression on mechanical behavior of Ti–10V–2Fe–3Al alloy produced by blended elemental powder metallurgy and containing a metastable β matrix with ~0.1 fraction of α phase was investigated. A detailed scanning transmission electron microscopy study revealed the initiation of slip and deformation-induced α′′ martensite and ωD formation at the beginning of plastic deformation in the stress plateau region of stress-strain curve. {332}<113> twinning occurred at a later stage. Deformation-induced ωD formed in the β matrix and within {332}<113> twins, but was consumed by other deformation products at strains exceeding 0.2. Formation of {112}<111> twins within {332}<113> twins and along their interfaces with the matrix was uncovered. The rate of development of deformation products among the β phase grains was non-uniform with many being fully transformed to α′′ martensite by 0.4 strain, whereas others experienced deformation conditions related to stress plateau region (<0.1 strain) and were only partially transformed. Formation of deformation-induced nanoscale ωD at the α′′ martensite/β interface was found only in the sample with more stable β matrix due to 0.26 fraction of α being present. This was related to a higher rigidity of the β phase resulting from the higher levels of alloying elements. This induced the triggering of β→ω transformation by stresses arising from α′′ martensite formation.

Synthesis of Ti/TiB Composites via Hydrogen-Assisted Blended Elemental Powder Metallurgy

Titanium–titanium boride (Ti/TiB) metal matrix composites have been widely identified as promising materials for various applications. The traditional ingot metallurgy processing strategies used to fabricate these materials are energy intensive and have fallen short of their perceived mass production potentials. Powder metallurgy processing, especially that aimed at in-situ synthesis of Ti/TiB composites from titanium and TiB2 powder blends, is currently widely used for cost-efficient production of such composites. However, this approach usually results in excessive sintered porosities and associated mechanical property degradation. Therefore, further thermomechanical or hot isostatic pressing (HIP) steps are required for porosity reduction. In the present study, low-porosity Ti/TiB composites were synthesized using TiH2 and TiB2 powders via a simple press-and-sinter hydrogen-assisted blended elemental powder metallurgy route. The manufacturing route included two stages. Compaction and vacuum sintering of the noted blended powders was followed by hydrogenation and ball milling of the pre-sintered product to produce a hydrogenated, pre-alloyed powder. This was followed by compaction and final sintering. X-ray diffraction (XRD), light microscope (LM), and scanning electron microscope (SEM) were employed to investigate the powder morphology and material microstructures after various processing steps. The role of temporary alloying with hydrogen was established in tailoring the microstructure. When an optimized particle size distribution that was carefully controlled using a Malvern Mastersizer laser analyzer was combined with optimized hydrogenated pre-alloyed Ti/TiB powder compaction and sintering parameters, a nearly dense, uniform composite was formed. The above approach can be considered a promising solution for economical manufacturing of Ti/TiB parts with improved properties, i.e., with high performance-to-cost ratios.

Friction welding of conventional Ti-6Al-4V alloy with a Ti-6Al-4V based metal matrix composite reinforced by TiC

Titanium alloys are supreme structural materials primarily due to their high specific strength. However, their wide use is largely restrained by the high cost of raw titanium compared to other metals commonly used in structural alloys. Layered structures of titanium alloys allow substantial increase of the material utilisation ratio and therefore draw significant attention. The rational ways of layered parts fabrication are bonding or joining of individually optimised layers into a final complex structure. The use of friction welding to join the parts is one of the most attractive ways of achieving a desirable result, since it is a solid state and near-net-shape process that modifies the structure of connected parts only locally. The study goal was to validate feasibility of the layered structures of Ti-6Al-4V (Ti-64) alloy and metal matrix composite (MMC) on its base with 10% of TiC fabricated by rotary friction welding (RFW) and linear friction welding (LFW). Both initial structures, Ti-64 and MMC, were made using low-cost blended elemental powder metallurgy. RFW and LFW were successfully used to bond the sections of the alloy and its composite. TiC particles stabilise the structure and are not fragmented by friction welding under used processing parameters.