This paper investigates the level of properties enhancement achievable by heat-treating Ti-6Al-4V alloy produced from a blended powder mixture using a thermomechanical powder consolidation route involving warm uniaxial pressing and vacuum sintering followed by extrusion at super transus temperature (1150 °C). The as-extruded material with a higher oxygen content of 0.55 wt.% was subjected to two different sub-transus annealing treatments: HT-A: 955 °C/1 h-furnace cooling and HT-B: 925 °C/4 h-cooling @ 50 °C/h to 760 °C-furnace cooling. Room temperature Charpy v-notch impact toughness tests and tensile tests were performed to ascertain the effect of microstructural changes during post-extrusion annealing treatments. After impact tests, analysis of microstructures and fracture surfaces of samples was carried out using optical and scanning electron microscopy. The as-extruded material displayed mean impact toughness of 4 J along with a yield strength of 956 MPa, an ultimate tensile strength of 1150 MPa, and an elongation to fracture of 2.4%. The annealing treatments gave a noticeable enhancement in the impact toughness (average values 5–6 J obtained) while maintaining a yield strength and ultimate tensile strength level of about 992 MPa and 1164–1181 MPa, respectively. Additionally, the level of change in ductility was limited for each sub-transus annealing treatment, and HT-A has given only a 30% increase compared to as-extruded material.

This study investigates the consolidation of pre-alloyed Ti-6Al-4V powder through thermomechanical processing that involves cold isostatic pressing, sintering, hot pressing and extrusion. The microstructural evolution, oxygen pick-up and tensile properties attained after each major consolidation step reveal that there was a significant oxygen pick-up during de-binding/sintering, hot pressing had improved strength/ductility by eliminating porosity and extrusion resulted in a relatively fine lamellar structure. Overall, as-extruded material had an oxygen content of 0.22 wt-%, impact toughness of 21 J, yield strength of 971 MPa, ultimate strength of 1124 MPa and ductility of 9-11% which is comparable to corresponding values reported in the literature. An investigation of fracture surfaces along with crack propagation behaviour highlights that ductile fracture was the predominant mode of failure.

In this study, a rapid powder consolidation method combining powder compact hot pressing and extrusion was utilized to consolidate relatively cheap, high impurity blended powder mixture Ti–6Al–4V alloy. The purpose of this work was to investigate whether a suitable microstructure deriving from a particular heat treatment balance out or compensate for the presence of high interstitial impurity contents. From mechanical property data attained, it was clear that annealing in high α–β region gave a much better combination of mechanical properties: impact toughness (14 J), yield strength (878 MPa), ultimate tensile strength (1092 MPa), and ductility/plastic strain (6.2%) compared to as-extruded material despite the presence of 0.44 wt% oxygen. Therefore, it can be concluded that optimization of microstructures provides improvement to the fracture related properties and Ti–6Al–4V produced in this way is suitable for less demanding applications. For further enhancement in properties, utilization of low oxygen starting powders is vital.

The mechanical properties of titanium and titanium alloys are very sensitive to processing, microstructure, and impurity levels. In this paper, a blended powder mixture of Ti-6Al-4V alloy was consolidated by powder compact extrusion that involved warm compaction, vacuum sintering, and hot extrusion. The as-processed material with an oxygen content of 0.34 wt.% was subjected to various annealing treatments. The impact toughness of heat-treated material was determined using Charpy V-notch impact testing at room temperature. An emphasis was placed on establishing a relationship among fracture behaviour, microstructure, and the resulting properties of tested material. From the results, it is apparent that the highest impact toughness value of 19.3 J was achieved after α/β annealing and is comparable with typical values given in the literature for wrought Ti-6Al-4V. In terms of fracture behaviour, it is quite apparent that the crack propagation behaviour of powder-produced material is rather complex compared with the limited amount of data reported for ingot counterparts.

Ti-5553 (Ti-5Al-5V-5Mo-3Cr, wt. %) alloy is a recently developed near β titanium alloy and it has a very good hardenability, good ductility and high strength. In this study, we discussed the feasibility of preparing Ti-5553 alloy by different processes from powder mixtures of hydride-dehydride titanium powder, elemental powders and master alloy powders, including (1) direct extrusion of powder compact in argon, (2) extrusion of the vacuum-sintered billet in air and (3) extrusion of the hot-pressed billet in air. XRD, OM and SEM were used to determine the phase constitutions and microstructures of the prepared Ti-5553 alloys, and mechanical test was performed to examine their mechanical properties. The results showed the microstructures and phase constitutions of Ti-5553 alloys were significantly affected by different processes, which resulted in the relevant mechanical properties. The effect of the selected heat treatment on the microstructures and properties of Ti-5553 alloy were investigated as well.

In this paper, we explored to prepare a multi-compositional titanium alloy, Ti-5Al-5V-5Mo-3Cr (Ti-5553), by powder compact extrusion from elemental powder mixtures, and investigate the microstructure variation during the synthesising process and after post heat treatments and the changes of mechanical properties. XRD, OM and SEM were used to analyse the phase constitutions and microstructures of the Ti-5553 alloy at different processing conditions, and tensile tests were conducted to examine their mechanical properties. The results showed that a homogeneous Ti-5553 alloy was successfully produced by powder compact extrusion from the powder mixtures, beta phase was mainly contained in the hot-pressed and 1200 degrees C-extruded Ti-5553 alloy and had an equiaxed microstructure. Different types of alpha phase precipitated from the beta matrix after heat treatment, and this significantly changed the microstructures and improved the mechanical properties of the extruded Ti-5553 alloy, with yield strength of 1250 MPa and ultimate strength of 1300 MPa for the alloy treated at 675 degrees C for 2 h, and the ductility of about 6.1% for the alloy treated at 780 degrees C for 2 h. (C) 2018 Elsevier B.V. All rights reserved.

In this paper, a Ti-6Al-4V rectangular bar was successfully produced from a 5kg blended powder mixture using an industrial scale extrusion facility. The elemental hydride-dehydride (HDH) titanium and 60Al-40V master alloy mixture was warm pressed and vacuum sintered prior to β extrusion in air. The as-processed material was characterised for compositional homogeneity, oxygen pickup, microstructure, tensile properties and fracture behavior. Variation in microstructure and properties along the length of the extruded bar were also studied. It was found that oxygen pickup mainly occurred during vacuum sintering of the green billet and consequently the as-extruded material had an oxygen content of 0.55 wt.%. The processed material had a typical lamellar morphology with some evidence of micro-cracks at high magnification. A significant deviation in prior β grain and α colony sizes was observed along the length of the bar, due to variations in extrusion temperature and cooling rate. Both grains and colonies became finer as the location changed from the tip of the extruded bar to the back end. The as-processed material had ultimate tensile strength in the range of 1068-1268 MPa and elongation to fracture of 1.2-4.5%, mainly due to the high oxygen content and non-optimised microstructure. Fractographic analysis was consistent with the variation in mechanical performances obtained.

Blended Elemental Powder Metallurgy is a very attractive method for producing titanium alloys, which can be formed near net shape and have freedom in composition selection. However applications are still limited due to affordability. In this paper, we will discuss a possible cost-effective route, combining vacuum sintering, extrusion, and heat treatment, to produce titanium alloys with similar or better mechanical properties than that of ingot metallurgy titanium alloys. The as-processed material with an oxygen content of 0.34 ± 0.005 wt.% was subjected to heat treatments such as β annealing plus ageing and α+β annealing without ageing to attain a typical lamellar/Widmanstätten/basketweave type structure with a large variation in terms of the microstructural features such as grain size, colony size, inter-lamellar spacing, thickness of grain boundary α, and size of individual lamellar. From mechanical property data attained here, it was apparent that annealing in high α-β region gave a much better combination of mechanical properties: yield strength (860-902 MPa), ultimate tensile strength (1060-1084 MPa) and ductility/plastic strain (11.5-13.6%). The hardness values of heat treated material varied between 346-376 Vickers hardness (36.8-44.5 Rockwell hardness).

Titanium alloys are very sensitive to thermal history and different microstructures are obtained depending on their chemistry, processing route and post-processing heat treatment. The objective of this paper is to characterise solution-treated Ti-6Al-4V alloy rods from microstructural investigations using optical and transmission electron microscopy (TEM) in addition to measurements of chemical composition and levels of impurity oxygen. From the results, it is clear that the compositions and oxygen concentration of the different rods, which varied between 0.34–0.36wt%, was consistent from one extrusion to another. TEM analysis of the as-extruded material with a fine lamellar microstructure indicates that the severe deformation and attendant dynamic recrystallization during and after hot extrusion did not give rise to any undesirable features that can degrade the ductility. Solution treatment above the β transus and subsequent ageing causes grain growth with grains containing a metastable martensitic structure (only α’ phase was present), some retained β and a limited formation of acicular secondary α. The α+β quenched and aged treatment gives a lamellar type morphology, but at the α interfaces there is retained β with some secondary α and potentially some α’ phase. In terms of mechanical behaviour, the data from v-notch Charpy impact tests and non-standard micro-tensile testing suggests that both water quenched and aged microstructures give a higher yield strength (~1022–1033MPa) and micro-hardness (388 HV), while the fracture-related properties such as estimated plastic strain and impact toughness were between 5–6% and 13.7J respectively. Overall, the level of mechanical properties reported here is better than that for typical values reported in the literature for as-cast material after similar solution treatments.

In this paper, two different powder compact extrusion processes were explored to rapidly produce Ti6-Al-4V alloys from the powder mixture of hydride-dehydride titanium powder, Al-V master alloy powder and elemental Al powder. The mechanical properties of the as-extruded Ti-6Al-4V alloys could achieve the yield strength of 1180-1200 MPa, the ultimate strength of 1215-1272 MPa and an elongation to fracture of about 10%, which could meet the requirements of most engineering applications. (C) 2016 Elsevier B.V. All rights reserved.

Ti-6Al-4V alloy powders produced using a hydrogenation–dehydrogenation process and a gas atomization process, respectively, were rapidly consolidated into near-net-shaped parts by powder compact forging. The porosity, microstructure, and tensile mechanical properties of specimens cut from regions at different distances from the side surfaces of the forged parts were examined. The regions near the side surfaces contained a fraction of pores due to the circumferential tensile strain arising during the powder compact forging process, and the porosity level decreased rapidly to zero with increasing the distance from the side surface. The forged parts had a fully lamellar structure with the α + β colony sizes and α lamella thickness changing little with the distance from the side surface. The specimens cut from the regions near the side surfaces had a lower yield strength and tensile strength. The correlation of porosity with the yield strength of the specimens suggested that the reduction of load bearing areas due to the porosity and unbonded or weakly bonded interparticle boundaries was not the only reason for the lower strength, and the stress concentration at the pores and associated with their geometry also played an important role in this. It is likely that the effect of stress concentration on yield strength reduction of the forged part increases with oxygen content. The Hall–Petch relationship of the yield strength and the average α lamella thickness suggested that the strength of the fully dense and fully consolidated forged parts was increased by oxygen solution strengthening.

A trace amount of LaB6 powder was added to P/M Ti and Ti–6Al–4V alloy to improve mechanical properties and refine the microstructure. After sintering, TiB whiskers and La2O3 dispersoids had formed in the microstructure. In a CP Ti alloy, the generation of secondary phases leads to a much refined microstructure, but the alignment of TiB whiskers led to a variation in mechanical properties. Open die forging (ODF) or powder compact extrusion (PCE) was carried out on sintered Ti–6Al–4V alloy to further improve the mechanical properties. This caused severe deformation and re-alignment of the TiB whiskers. Comparing the properties of hot worked Ti–6Al–4V alloy and Ti–6Al–4V alloy with boron additions, an addition of LaB6 leads to slightly lower strength but gives significant better ductility.

Powder compact forging in combination with induction sintering, a field assisted sintering technique (FAST), was used to produce commercially pure (CP) Ti and Ti-13V-11Cr-3Al parts. Green powder compacts with high relative density were manufactured by cold compaction and warm compaction, respectively. During the powder compact forging process, CP titanium powder was consolidated completely to produce a near net shaped top cover for a diving helmet with full density and good mechanical properties. Also, a Ti-13V-11Cr-3Al alloy was fully consolidated into a cylinder using blended elemental powders. As a comparison, raw titanium powder with different oxygen contents was used to make a Ti-13V-11Cr-3Al powder compact forging. Using a starting powder with low oxygen content, a forged cylinder with good mechanical properties was produced.

Powder compact extrusion (PCE) is an innovative way of processing titanium and titanium alloys to produce good-quality material with a wide range of compositions, microstructures and mechanical properties. This paper explores PCE processing of Ti-6Al-4V alloy prepared from a blended powder mixture, containing elemental hydride-dehydride (HDH) titanium powder and master alloy (60Al-40V) powder. The warm pressed compacts of blended powders were sintered using a vacuum sintering furnace prior to β extrusion. The resulting material was used to measure the performance under high strain rate and tri-axial stress state using Charpy v-notch testing. A comparison was made of the microstructure after vacuum sintering and hot extrusion in addition to oxygen measurements to determine the degree of oxygen pickup during each processing stage. A comprehensive study of fracture surfaces in selected samples was carried out using optical microscopy and scanning electron microscopy. Based on the results, it is clear that certain samples picked up varying amounts of interstitial impurities during processing and as a consequence a significant number of micro-cracks were observed in lamellar type microstructures. The oxygen content of all as-extruded samples was between 0.34-0.44 wt.% with resultant impact toughness in the range of 10-14 J. The best impact toughness attained for the lowest oxygen as-extruded rods was 20% lower than the literature values for wrought material. In terms of fracture behaviour, ductile dimples, cleavage facets and cracks passing through lamellar structures were observed in all samples. However, the quantity of these fracture features varied significantly in each sample.

Hydride-dehydride (HDH) Ti powder was consolidated into fully dense parts of rocker arms for internal combustion engines by powder compact forging at 1350 °C. The microstructure, tensile mechanical properties and fracture behavior of forged Ti parts were studied. It was found that fully dense forged Ti parts had a fine α lamellar structure, and increasing the holding time of the powder compact at 1350 °C from zero to 5 min and post-forging annealing at 550 °C for 6 h are two effective ways to improve the level of consolidation of the Ti parts by removing weakly bonded interparticle boundaries (IPBs), leading to a significant increase of their ductility. The former approach is a better way of improving the level of consolidation due to the fact that it does not cause significant microstructure coarsening and clear decrease of tensile strength of the Ti parts. The correlation between the yield strength of the forged Ti parts without and with annealing and their average α-Ti lamellar thickness shows that it follows the Hall–Petch relationship, and the sensitivity of the yield strength of α-Ti to the average lamellar thickness is clearly higher than its sensitivity to the average size of equiaxed grains.

Blended Elemental Powder Metallurgy (BE-PM) is a very attractive method for producing titanium alloys, which can be near-net shape formed with compositional freedom. However, a minimization of oxygen pick-up during processing into manufactured parts is a big challenge for powder metallurgy of titanium alloys. In this paper, different approaches for preparing titanium alloy parts by powder compact extrusion with 0.05-0.1wt.% of oxygen pick-up during manufacturing are discussed. The starting materials were a powder mixture of HDH titanium powder, other elemental powders and a master alloy powder. Different titanium alloys and composites, such as Ti-6Al-4V, Ti-4Al-4Sn-4Mo-0.5Si, Ti-5Al-5V-5Mo-3Cr, and Ti-5Al-5V-5Mo-3Cr-5vol%TiB, with different profiles such as round and rectangular bars, a wedge profile, wire and tubes have been successfully manufactured on a laboratory and pilot-plant scale. Furthermore, a possible route for scaling up the titanium processing capabilities in the University of Waikato has also been discussed.

This research focuses on the development of low cost powder metallurgy (PM) Ti alloys suitable for application in PM thermomechanical processing with mechanical properties comparable to those of wrought Ti6Al4V alloy. The alloy systems studied are Ti3Al2V, Ti5Fe and Ti3.2Fe1Cr0.6Ni0.1Mo (Ti5SS). The alloy mixtures were produced by blending Ti HDH powders with Al40V, 316SS master alloy powders or elemental Fe powder. The blended powders were further consolidated using various methods: high vacuum sintering (HVS), induction sintering (IS), powder compact forging (PCF) and powder compact extrusion (PCE). It is found that, PM Ti3Al2V and Ti5Fe alloy processed by PCE or PCF followed by recrystallization annealing (RA) achieved tensile properties comparable with wrought Ti6Al4V alloy. Tensile properties such as yield strength (YS) of 910MPa, UTS of 1010MPa and 15% elongation to fracture for Ti3Al2V alloy are reported. Ti5Fe alloy gives YS and UTS of 870MPa and 968MPa respectively, combined with 20.3% elongation to fracture. The tensile results are related to the microstructure developed during the consolidation processes. The oxygen contamination as a result of the high temperature processing is also reported.

In this paper, pure titanium rods, with high strength and ductility, were prepared by vacuum sintering titanium powder compacts at 1300oC for 2h and then hot extruding the as-sintered titanium billets at 900oC in air. The microstructure and property changes, after vacuum sintering and hot extrusion, were investigated. The results showed clear evidence of porosity in the microstructure of as-sintered titanium billet and tensile testing of as-sintered material gave yield strength, ultimate tensile strength and ductility values of 570MPa, 602MPa and 4%, respectively. After extrusion at 900oC, no obvious pores could be seen in the microstructure of as-extruded titanium rod, and the mechanical properties were significantly improved. The yield strength, ultimate tensile strength and the ductility reached 650MPa, 705MPa and 20%, respectively, which are much higher than values for CP titanium (grade 4), with a yield strength of 480MPa, ultimate tensile strength of 550MPa and ductility of 15%. The fracture characteristics of as-sintered and as-extruded titanium rods have also been investigated.