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.
The effects of lamellar features on the fracture toughness of Ti-17 titanium alloy are studied in the present paper. Three cooling methods were used to prepare different lamellar features of Ti-17 ...titanium alloy after β forging. Then the same solid solution plus aging treatment were conducted to get the final microstructures. The results show that the microstructure with long and thick needle-like α platelets gets higher fracture toughness as well as strength than the microstructure with short rod-like α platelets. This seemingly “abnormal” phenomenon can be explained based on the theory that the fracture toughness is attributed to two major contributions, namely the crack path tortuosity (extrinsic part) and material plastic deformation along the crack path (intrinsic part). The respective contribution of the plasticity and crack path tortuosity to the fracture toughness of Ti-17 alloy are quantitatively evaluated based on the existent models proposed by previous researchers. The results show that the intrinsic contributions for the three microstructures with different lamellar features do not show a big difference. However, their extrinsic contributions are dramatically different. The microstructure which contains the longest and thickest α platelets gets the most rugged crack propagation path and moderate plasticity among the three microstructures, which results in the highest fracture toughness. Moreover, due to the nature of the near-β Ti-17 alloy, the long and thick α platelets in microstructure also get high aspect ratios, which results in high interfacial strengthening effect. Thus for Ti-17 alloy studied in the present work, the long and thick α platelets in microstructure can realize a good combination of fracture toughness and strength.
The impact toughness of titanium alloys is one of the key factors determining their safe service in cryogenic temperature environments. In this work, the temperature-related impact properties of ...grade 2 pure titanium and Ti-2.5Al–3Zr–1Mo alloys are investigated. It is found that the impact properties and deformation mechanisms of the above two materials are different with decreasing temperature (20 °C, 0 °C, −50 °C, −100 °C and −196 °C). Speaking of pure titanium: the impact toughness doesn't change obviously, and crack initiation energy (Wi) gradually increases while crack propagation energy (Wp) decreases (Wp of −196 °C is 40% lower than that of 20 °C while Wi is 90% higher). The slip-dominated deformation mechanism at 20 °C gradually transforms into twinning-dominated deformation mechanism under cryogenic temperature. High-density twins formed at −100 °C and −196 °C can effectively relieve stress concentration and lead to better cryogenic impact toughness. By contrast, Wi and Wp of Ti-2.5Al–3Zr–1Mo alloy decrease with decreasing temperature. The impact toughness of Ti-2.5Al–3Zr–1Mo alloy is higher than that of pure titanium when the temperature is above −100 °C. At 20 °C, the synergistic effect of the tortuous crack path and deformation twins of Ti-2.5Al–3Zr–1Mo alloy promotes its impact toughness higher than that of pure titanium. However, the twinning density of Ti-2.5Al–3Zr–1Mo at −196 °C is much lower than that of pure titanium, which cannot release stress effectively and cause a brittle fracture. The research provides theoretical and experimental basis for the application of titanium alloys in cryogenic environment, and provides guidance for the development of titanium alloys with better cryogenic impact toughness.
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•The Ti2Cu of corrosion activity is composed of a “micro-galvanic cell” with α-Ti.•The lamellar Ti2Cu increased the Cu ion release caused by more galvanic interface.•The antibacterial ...rate of L-Ti2Cu is 99.5 %, due to the rapid release of Cu ions.
The influence of morphology of the Ti2Cu phase on biological corrosion and antibacterial properties of Ti-Cu alloy was investigated by micro-galvanic corrosion. Elongated “micro-galvanic cells” were formed between lamellar Ti2Cu phase (L-Ti2Cu) and α-Ti matrix due to the different Volta potentials. The corrosion rate (Vcorr) of L-Ti2Cu was twice that of granular Ti2Cu phase (G-Ti2Cu) because lamellar Ti2Cu phase had more galvanic interface. The release of Cu2+ ions in L-Ti2Cu was 55 % higher than G-Ti2Cu, reaching 99.5 % of the antibacterial rate in L-Ti2Cu and providing a great potential in clinical application for dental implants.
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.
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•A toughened ZrO2/MgO nanocomposite coating is in-situ synthesized during the plasma electrolytic oxidation process (PEO).•The ZrO2/MgO toughening behavior occurs with dislocation ...slipping and pinning caused by semicoherent interface lattice distortion.•The toughness (KIC) of the ZrO2/MgO nanocomposite coating is 2.7 times that of the traditional PEO coating.
Ceramic coatings are in general a kind of brittle material because they are predominantly made up of ionic crystals that avoid dislocation motion caused by lattice distortion. In this regard, a remarkable toughened ZrO2/MgO nanocomposite coating is obtained by the plasma electrolytic oxidation (PEO) process and in-situ synthesized ZrO2 with quantitative control approach. It is revealed that the toughening behavior of the ZrO2/MgO coating is related to the coordination and diversion of lattice distortion at the metallic oxide interface, which induces distinct dislocation motion at the interface. The semicoherent interface between m-ZrO2 and MgO is verified to act as a buffer to realize toughening of the nanocomposite coating through dislocation slipping induced by lattice coordinated distortion. Simultaneously, significant interfacial lattice distortion transfer and dislocation pinning are discovered at the semicoherent interface between t-ZrO2 and MgO, which are beneficial to toughness enhancement of the nanocomposite coating. The results indicate that the toughening effect occurs along with dislocation slipping and pinning caused by lattice distortion of the ZrO2/MgO semicoherent interface, which enables the toughness of novel nanocomposite coating to reach 2.7 times of the traditional PEO coating.
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•The CT20 alloy with a special texture shows simultaneous improvement in strength and ductility at cryogenic temperature.•More twin types are activated at 77 K and continuous ...formation of twin boundaries causes the dynamic Hall-Petch effect.•The < -12–11>//ND texture and strong TWIP effect cause excellent ductility at cryogenic temperature.•Cryogenic temperature changed the locations of crack initiation in CT20 alloy with equiaxed microstructure.
Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a <-12-11>//ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial <-12-11>//ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.
Titanium alloys are widely used in aerospace, chemical, biomedical and other important fields due to outstanding properties. The mechanical behavior of Ti alloys depends on microstructural ...characteristics and type of alloying elements. The purpose of this study was to investigate the effects of different Cu contents (2.5 wt.%, 7 wt.% and 14 wt.%) on mechanical and frictional properties of titanium alloys. The properties of titanium alloy were characterized by tensile test, electron microscope, X-ray diffraction, differential scanning calorimetry, reciprocating friction and wear test. The results show that the intermediate phase that forms the eutectoid structure with α-Ti was identified as FCC Ti2Cu, and no primary β phase was formed. With the increase of Cu content, the Ti2Cu phase precipitation in the alloy increases. Ti2Cu particles with needle structure increase the dislocation pinning effect on grain boundary and improve the strength and hardness of titanium alloy. Thus, Ti-14Cu shows the lowest elongation, the best friction and wear resistance, which is caused by the existence of Ti2Cu phases. It has been proved that the mechanical and frictional properties of Ti-Cu alloys can be adjusted by changing the Cu content, so as to better meet its application in the medical field.
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•The negative linear correlation between phase transition temperature and grain size of t-ZrO2 was established.•t-ZrO2 achieves phase stability, which cannot occur martensitic ...transformation when grain size below the critical size.•The dislocation tangle and interfacial cohesion enhance the stability of t-ZrO2.
In this work, the trade-off between transformation toughening of ZrO2/TiO2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO2 (dt-ZrO2). A negative correlation between dt-ZrO2 and phase transition temperature (Ms) was also established based on strain energy and chemical free energy in ZrO2/TiO2 ceramic coatings. Interestingly, t-ZrO2 grains lost toughening effects when the dt-ZrO2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the dt-ZrO2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (011) t-ZrO2 and (110) TiO2 was enhanced and t-ZrO2 was completely stabilized when dt-ZrO2 reaches critical size. This work elucidates the effect of size effect on Ms and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature.
Understanding the mechanisms of deformation and fracture of metastable β titanium alloys is of great significance for improving formability and service life. By combining the in-situ tensile test, ...TEM characterization and EBSD analysis, the tensile deformation behavior, activation of slip systems, crack initiation, and propagation of a high strength metastable β titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with equiaxed microstructure are investigated. The equiaxed microstructure is composed of primary α (α
) phase, transformed β (β
) matrix phase, and secondary α (α
) phase. In contrast to the hexagonal α
grain with limited slip systems, the body-centered β
matrix has more slip systems, however the hindering effect of α
phases on dislocation slip leads to the different deformability of the α
phase and β
matrix. The equiaxed α
grains are more prone to deformation and rotation to coordinate the overall deformation. The shear band leads to the formation of sub-grain boundary and even the fragmentation of α
grains. As a result, the microvoids tend to nucleate at the grain boundary, phase interface, slip band, and shear band. The inhomogeneous deformation in the plastic deformation zone around the crack tip is the primary cause of damage. The crack propagation caused by microvoids coalescence advances along the grain boundaries and phase interfaces in the form of intergranular, and along the activated slip systems and shear bands in the form of transgranular. Pinpointing the situation in the equiaxed microstructure and combining that in other typical microstructures will help to summarize the universal deformation and fracture mechanisms of metastable β titanium alloy, and provide a basis for alloy design and microstructure tailoring.
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