To realize the systematic comparison of the hot workability and guide the further hot-processing of powder metallurgy (PM) and ingot metallurgy (IM) Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloys, the hot ...deformation behaviour and microstructural evolution of the two alloys were investigated at a wide temperature range of 700 °C–1100 °C and strain rate of 0.001 s−1-10 s−1. The activation energy maps and processing maps for both PM and IM alloys were constructed, as well as the specific deformation mechanisms were identified for each processing region. The results showed that PM alloy has lower deformation resistance, smaller activation energy and larger optimal processing windows than those of IM alloy. The dynamic α precipitation mechanisms in PM alloy were diffusional globularization and coarsening, rather than diffusionless shearing and fracturing in IM alloy. The extensive dynamic recrystallization (DRX) happened at 900 °C–1050 °C for PM alloy and at 1000 °C–1100 °C for IM alloy. The DRX process was dominated by discontinuous dynamic recrystallization (DDRX) for PM alloy while continuous dynamic recrystallization (CDRX) for IM alloy. Furthermore, PM alloy had smaller flow instability region than IM counterpart in the hot processing map. The schematic deformation mechanism maps were eventually developed for both PM and IM Ti-5553 alloys.
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•Ti-5553 alloy with better workability than ingot-casting (IM) counterpart was prepared by fast powder-consolidation (PM).•Activation energy maps and processing maps of PM and IM alloys were constructed to evaluate their hot workability.•Comprehensive comparison of deformation mechanisms of the alloys is achieved by the deformation mechanism maps.•Different dynamic recrystallization mechanisms were identified in PM and IM alloys.•Different dynamic α precipitation mechanisms were verified and characterized in PM and IM alloys.
Short-time processing route has been designed to manufacture cost-affordable and high-quality powder metallurgy (PM) metastable β titanium alloy, containing rapid powder consolidation (modified ...thermomechanical pressing), one-step thermomechanical processing (simple open die uniaxial hot forging by industrial press) and fast heat treatment (one-step annealing at various temperatures for only one hour). Based on comprehensive microstructure characterizations and mechanical property examinations, underlying microstructural evolution mechanism and microstructure-property relationship of the produced alloys were uncovered and elucidated thoroughly. Homogeneous macrostructure and fine-grain microstructure without undissolved particles and large pores are obtained for the alloy after thermomechanical powder consolidation as a result of the concurrent effect of external deformation and high-temperature diffusion. One-step open-die forging is verified to produce full-dense and sound PM alloy pancake with large-scale and high strength. Attributed to the harmonious concurrence of hierarchical α precipitation and heterogeneous grain structure, synergistic strength-ductility combinations are achieved for the alloy after specific processing and heat treatment with the tensile strength and strain at failure values of 1386.5 MPa/7.3% and 1252.3 MPa/9.0%, respectively. These strength-ductility combinations are comparable and/or even better than other metastable β titanium alloys prepared by some PM and ingot metallurgy approaches with relatively high cost and time consumption.
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•Short-time processing route is designed to produce cost-affordable and high-quality powder metallurgy titanium alloy.•Rapid consolidation, one-step processing and fast heat treatment are applied to minimize the manufacturing cost and time.•Superior strength-ductility combinations are achieved for the alloy after specific processing and fast heat treatment.•The excellent mechanical properties are comparable to other expensive and time-consuming metastable β titanium alloys.
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.
The hot workability of metallic materials is significantly dependent on its ability to form plastic without cracking and fracturing. In this work, the cracking behavior of powder metallurgy (PM) ...Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloy, consolidated from powder mixture, at a deformation temperature range of 600 °C⁻850 °C and strain rate of 0.1 s
⁻10 s
, was investigated through isothermal compression tests. The cracking behavior of the as-cast ingot metallurgy (IM) Ti-5553 alloy, at a deformation temperature of 700 °C was also investigated for comparison. Results suggested that the PM Ti-5553 alloy had a better hot workability, with a larger cracking-free processing window, and a lower deformation resistance than the IM counterpart. 45° shear fracture occurred in the PM alloy, compressed at the condition of 600 °C/10 s
, and edge cracking was observed at the 700 °C/10 s
. 45° shear fracture was also significant in the IM alloy specimen tested at 700 °C/10 s
, and all the other IM alloy specimens compressed at 700 °C displayed longitudinal cracking. Moreover, the microscopic cracking observation showed that ductile dimple cracking can be found in the IM alloy, but brittle cleavage fracture was dominant in the cracking surface of PM alloy with a relatively low cracking ductility.
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.
Isothermal compression tests of Ti-5553 (Ti-5Al-5V-5Mo-3Cr) alloy, produced by a fast consolidation approach from blended elemental powder mixture, were performed on a Gleeble® 3800 thermal-physical ...simulator to investigate its hot deformation behaviour. The samples were compressed in a wide temperature range from 700 ºC to 1150 ºC and a moderate-high strain rate of 1 s-1, with the sample deformation degree of 30%, 50% and 70%, respectively. Flow instability occurred when the deformation temperature was less than 900 ºC. Dynamic recovery (DRV) accompanied by dynamic recrystallization (DRX) become the dominated mechanisms at the medium temperature range between 900 ºC and 1000 ºC, while almost only DRV features could be observed at high temperature (1050 ºC ~ 1150 ºC). Moreover, α phase globalization could be identified in the alloy deformed in (α+β) region. DRV, DRX, α globalization and the transformation of α to β phase were promoted with the increasing deformation degree.
The comparisons of mechanical properties and fracture behaviour between as-consolidated PM Ti-5553 alloy and as-cast IM Ti-5553 alloy were investigated through tensile, fracture toughness and impact ...toughness tests in this research. The slightly higher strength but much higher ductility and toughness can be identified in IM alloy specimens, which is also confirmed by the fracture behaviour of the specimens after mechanical tests. IM alloy specimens always exhibit the ductile dimple fracture mechanism in the different tests, while the fracture mechanism of PM alloy specimens indicates a high loading rate sensitivity, changing from the mixed ductile-brittle quasi-cleavage fracture into the brittle cleavage fracture mechanism accompanied by the remarkable decrease of impact toughness. The relatively low mechanical properties, especially the ductility and the brittle fracture behaviour of as-consolidated PM Ti-5553 alloy, are mainly explained by the differences in the initial microstructures between these two alloys.
The plastic deformation processes and fracture mechanisms of as-consolidated powder metallurgy (PM) and as-cast ingot metallurgy (IM) metastable beta titanium alloys (Ti-5Al-5V-5Mo-3Cr) were ...thoroughly investigated by room temperature tensile tests with in-situ scanning electron microscopy (SEM) observations and further microstructure characterizations including transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results suggested that IM alloy has a better compatible deformation capability than PM alloy characterized by varying slip deformation mechanisms and the constantly changing slip modes. The microcracks in PM alloy were observed to be originated at the interfaces of α″/β and grain boundary α/β. Whereas, the microcracks in IM alloy were observed on the grain boundaries and the intracrystalline α precipitation areas, where the slip steps were generated. Particularly, the common defects in PM (residual pores and microvoids) and IM (casting cavity) alloys did not exhibit significant negative effects, contrary to previous awareness. Finally, the coalescence of the grain boundary α and the widened α″/β microcracks led to the sudden brittle transgranular-intergranular mixed fracture of PM alloy. For IM alloy, the serious cracking initiated the V-shape notch made its way through the microcracks at the α/β slip steps, resulting in the gradual transgranular fracture with better ductility.
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.
Ti-5Al-5V-5Mo-3Cr metastable beta titanium alloy was prepared by rapid thermomechanical powder consolidation approach from blended elemental powder mixture. Allotropic phase transformation and ...high-temperature tensile behaviour of the consolidated powder metallurgy Ti-5553 alloy were investigated in this work. The studied alloy has a high β phase transformation temperature of 975 °C±5 °C, which is higher than other conventional ingot metallurgy Ti-5553 alloys. The β grains in the microstructure of the alloy are coarsened significantly with increasing the heating temperature from 890 °C to 1050 °C, however, the grain coarsening tendency is mitigated when the heat treatment temperature reach to the range of 1080 °C–1100 °C. The high-temperature tensile mechanical properties of the alloy are sensitive to both the deformation temperature and strain rate, and superplastic deformation of the alloy was achieved at the condition of 850 °C/0.001 s−1 with the tensile elongation of 103.5%. The microstructural evolution characteristics and the fracture mechanisms of the alloy are varied with changing the deformation variables, which are revealed by the microstructure observation of the fractured specimens from different sampling positions.
•Metastable β titanium alloy was prepared by thermomechanical powder consolidation.•The PM alloy has a higher β phase transus of 975 °C±5 °C than IM counterparts.•Microstructure evolution and fracture mechanisms changes with deformation variables.•Superplastic deformation of the alloy is achieved at 850 °C/0.001 s−1.
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