Evolution laws of microstructures and mechanical properties during heat treatments for near-αhigh-temperature titanium alloys

Evolution laws of microstructures,mechanical properties,and fractographs after different solution temperatures were investigated through various analysis methods.With the increasing solution temperatures,contents of the primaryαphase decreased,and contents of transformedβstructures increased.Lamellarαgrains dominated the characteristics of transformedβstructures,and widths of secondaryαlamellas increased monotonously.For as-forged alloy,large silicides with equiaxed and rod-like morphologies,and nano-scale silicides were found.Silicides with large sizes might be(Ti,Zr,Nb)_(5)Si_(3) and(Ti,Zr,Nb)_(6)Si_(3).Rod-like silicides with small sizes precipitated in retainedβphase,exhibiting near 45°angles withα/βboundaries.Retainedβphases in as-heat treated alloys were incontinuous.980STA exhibited an excellent combination of room temperature(RT)and 650°C mechanical properties.Characteristics of fracture surfaces largely depended on the evolutions of microstructures.Meanwhile,silicides promoted the formation of mico-voids.

Influences of boron contents on microstructures and mechanical properties of as-casted nearαtitanium alloy

Ti-6.5 Al-2.5 Sn-9 Zr-0.5 Mo-0.25 Si-1 Nb-1 W-0.1 Er-x B(x=0,0.1,0.2,0.4,0.6 and 0.8 wt%)with different boron contents are fabricated for investigation.Influences of boron element and its amounts on phase constitutions,microstructures,textures and compression mechanical properties are carefully studied.With the increasing boron additions,contents of TiB phase increase,and the maximum intensities of textures decrease.Microstructures are significantly and continuously refined after adding boron element and with the increasing boron additions,and turning point of refinement rates for different microstructural parameters is found at 0.2 wt%boron content.Strengths increase monotonously,while elongations increase firstly and decrease afterwards.The maximum value of elongation is acquired at boron content of 0.2 wt%.On the premise of ensuring plasticity,0.2 wt%boron content is the most appropriate amount for microstructural refinement and mechanical properties enhancement for current nearαtitanium alloys.Meanwhile,aspect ratios of TiB whiskers increase with the increasing boron contents.Lots of near equiaxedαgrains orαgrains with irregular morphologies are discovered around TiB phase.Distorted and twistedαgrain boundaries are also obviously detected in boron containing alloys.Moreover,premature fracture of alloys containing TiB whiskers is largely influenced by the fracture of these brittle reinforcements.