Fatigue crack growth as a function of a phase volume fraction in Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy was investigated using fatigue testing, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The α+β annealing treatments with different solid solution temperatures and cooling rates were conducted in order to tailor microstructure with different a phase features in the Ti-6242 alloy, and fatigue crack growth mechanism was discussed after detailed microstructure characterization. The results showed that fatigue crack growth rate of Ti-6242 alloy decreased with the decrease in volume fraction of the primary α phase (αp). Samples with a large-sized a grain microstructure treated at high solid solution temperature and slow cooling rate have lower fatigue crack growth rate. The appearance of secondary a phase (αs) with the increase of solid solution temperature led to crack deflection. Moreover, a fatigue crack growth transition phenomenon was observed in the Paris regime of Ti-6242 alloy with 29.8% αp (typical bi-modal microstructure) and large-sized a grain microstructure, owing to the change of fatigue crack growth mechanism.

The influence of microstructure on creep behavior of Ti–5Al–5Mo–5V–1Fe–1Cr (TC18) alloy at 350–500 °C and tensile stress of 200–400 MPa was investigated by creep testing and transmission electron microscope (TEM). The creep mechanism was discussed by microstructure evolution. The results showed that, the alloy with lamellar structure showed better creep resistance than that of equiaxed structure. At 350–400 °C, the stress exponent n   of samples with both structure was in the range of 1.2–1.9, the creep was controlled by a/3〈112¯0〉 dislocations gliding on {101¯0} prism plane, {0002} basal plane and {101¯1} pyramidal plane. The creep activation energy of samples with both structure increased from 119 to 364 kJ/mol, with the increase of tensile stress from 200 to 400 MPa. At 450 °C, the stress exponent n of samples with both structure was about 3.0. At 500 °C, n is 4.3–4.8 under lower tensile stress, and 8.2–8.5 under higher tensile stress. At 450 °C and 500 °C, there was a dramatical rise of total creep strain, the jogged dislocation glided on {0002} basal plane was dominated, and the creep was controlled by dislocation climb.

•The ωathin quenched alloy transformed to ωisoor α at different temperatures.•ST alloy with ωath + β microstructure showed 80 GPa modulus and 20% elongation.•The alloy was highly embrittled by the ωisoand α phases formed during aging.•The ST alloy showed better corrosion resistance than Ti-6Al-4 V alloy.A biomedical β titanium alloy (Ti–7Nb–10Mo) was designed and prepared by vacuum arc self-consumable melting. The ingot was forged and rolled to plates, followed by quenching and aging. Age-hardening behavior, microstructure evolution and its influence on mechanical properties of the alloy during aging were investigated, using X-ray diffraction, transmission electron microscopy, tensile and hardness measurements. The electrochemical behavior of the alloy was investigated in Ringer's solution. The microstructure of solution-treated (ST) alloy consists of the supersaturated solid solution β phase and the ωath formed during athermal process. The ST alloy exhibits Young's modulus of 80 GPa, tensile strength of 774 MPa and elongation of 20%. The precipitation sequences during isothermal aging at different temperatures were determined as β + ωath → β + ωiso (144 h) at Taging = 350–400 °C, β + ωath → β + ωiso + α → β + α at Taging = 500 °C, and β + ωath → β + α at Taging = 600–650 °C, where ωiso forms during isothermal process. The mechanical properties of the alloy can be tailored easily through controlling the phase transition during aging. Comparing with the conventional Ti-6Al-4 V alloy, the Ti–7Nb–10Mo alloy is more resistant to corrosion in Ringer's solution. Results show that the Ti–7Nb–10Mo alloy is promising for biomedical applications.

Multilayer coatings composed of TiN, TiCN, α-Al2O3 and κ-Al2O3 were designed and then deposited on WC–Co alloy by chemical vapor deposition (CVD) technique, the samples of WC–Co alloy with multilayer coatings were oxidized in the temperature range of 600 °C–950 °C for various times in a Muffle furnace, and weight gain was measured by electronic balance. Phase component and microstructure evolution of coating samples after oxidation were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the oxidation resistance of WC–Co alloy was improved markedly after deposition of multilayer coatings. The oxidation kinetics of multilayer coating samples obeyed linear law and diffusion-controlled parabolic law at different oxidation conditions. The oxidation product of coatings was rutile TiO2. The sample exhibited excellent oxidation resistance when the outermost layer was α-Al2O3, which was consistent to the results of apparent activation energy of oxidation reaction. The oxidation resistance of multilayer coatings was improved with the increase of thickness of κ-Al2O3 layer. The κ-Al2O3 transformed into α-Al2O3 over 900 °C. The interface between TiN and TiCN disappeared in the coating sample without α-Al2O3 and κ-Al2O3 layer.Highlights► The new type multilayer coatings were designed and successfully deposited on WC–Co hard metal. ► The oxidation mechanism and kinetics were revealed for our new type coatings. ► The results showed that the multilayer coatings taking α-Al2O3 as outermost layer had excellent oxidation resistance.