J. C. Williams

The effect of ternary additions on the decompositon of metastable beta-phase titanium alloys

The effect of ternary additions of Al, O, Sn, and Zr on the decomposition of metastable Ti-Mo and Ti-V Β-phase alloys has been studied. It is shown that all these additions reduce the volume fraction, upper temperature limit of formation, and time of stability of the Ω phase. These results have been contrasted to earlier work in binary alloys in which misfit was shown to be a primary factor in determining the morphology and range of stability of the Ω phase. In the ternary alloys the particle morphology can still be explained in terms of misfit, but other considerations appear to be predominant in determining the range of stability. Results are also presented on a phase separation reaction which occurs at higher alloy contents and which has an important influence on the morphology of α-phase precipitation.

The ω-phase as an example of an unusual shear transformation

The conditions leading to formation of the metastable ω-phase in Ti, Zr, and Hf alloys are described and earlier experimental observations directly related to ω -phase formation are summarized. New experimental results are presented which show that increased oxygen content suppresses athermal ω-phase formation in Ti-V alloys. A mechanism of ω-phase formation based on the formation of a linear displacement defect is described and it is shown that both the earlier and new experimental results are consistent with this mechanism. Additional experimental results on variations in electrical and physical properties in Ti alloys are also shown to be consistent with the linear displacement defect model.

The effect of omega phase on the mechanical properties of titanium alloys

The effect of the precipitation of the metastable ω phase on the tensile properties of β-phase titanium alloys has been studied. The volume fraction of ω phase was varied by controlling the heat treatment temperature and the alloy content. It is shown that provided the volume of ω phase is less than 0.6, significant increases in yield strength can be obtained while retaining reasonable ductility. Higher volume fractions results in complete macroscopic embrittlement, but fracture still occurs by microvoid coalescence. Thin film microscopy of deformed samples shows that dislocations bypass the omega particles. The results are discussed in relation to current theories of deformation and fracture of two-phase alloys.

The microstructure of ti alloys as influenced by Thin-Foil artifacts

Abstract : The occurrence of a variety of thin foil artifacts which form during preparation of electron microscope thin foils from Ti alloys have been described in the literature. These artifacts severely complicate the study of phase transformations and microstructure/property relations in Ti alloys. This paper illustrates several examples of such artifacts which occur in a wide range of alloys and show how their presence can be bothersome and, in some instances, grossly misleading. Examples include spontaneous relaxation in beta-phase alloys, reversion of martensite and modification of omega-phase precipitates. An ion-thinning technique has been developed which suppresses the occurrence of thin foil artifacts, thereby permitting examination of alloys and microstructures which previously have not been analyzed. The structures of ion-thinned samples are illustrated and compared to the structures observed in conventionally thinned samples. (Author)

The morphology and substructure of Ti-Cu martensite

AbstractThe martensites in Ti-Cu alloys containing up to 8 wt pct Cu have been examined using transmission electron microscopy techniques. The martensite has a massive morphology in the alloys which contain 4 pct Cu or less, whereas the alloys containing 6 and 8 pct Cu exhibit acicular martensite. Experimental evidence is presented to show that the lattice invariant deformation in the massive martensite occurs by internal slip with a Burgers vectorn

The Eutectoid Region of the Ti-Pd System

1/3[2bar 1bar 13]

Accurate description of slip character

n and these results are discussed in terms of recent calculations. The transition from the massive to acicular martensite morphology is also discussed.

The effect of hydrogen on the strength, modulus and lattice parameter of a TiMo alloy

AbstractThe precipitation processes that accompany the aging of supersaturatedα-titanium solid solutions containing up to 6 wt pct Cu have been studied by thin foil electron microscopy and X-ray diffraction techniques. Two mechanisms of decomposition have been identified: i) the heterogeneous nucleation and growth of Ti2Cu at interfaces and internal substructure such as dislocations, and ii) the uniform nucleation of thin, coherent, disk-shaped precipitates which lie onn% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaai4Eaiaaig% dacaaIWaWaa0aaaeaacaaIXaaaaiaaigdacaGG9baaaa!3AE9!nn