Segregation mediated heterogeneous structure in a metastable β titanium alloy with a superior combination of strength and ductility

Abstract

In β titanium alloys, the β stabilizers segregate easily and considerable effort has been devoted to alleviate/eliminate the segregation. In this work, instead of addressing the segregation problems, the segregation was utilized to develop a novel microstructure consisting of a nanometre-grained duplex (α+β) structure and micrometre scale β phase with superior mechanical properties. An as-cast Ti-9Mo-6W alloy exhibited segregation of Mo and W at the tens of micrometre scale. This was subjected to cold rolling and flash annealing at 820 oC for 2 and 5 mins. The solidification segregation of Mo and W leads to a locally different microstructure after cold rolling (i.e., nanostructured β phase in the regions rich in Mo and W and plate-like martensite and β phase in regions relatively poor in Mo and W), which play a decisive role in the formation of the heterogeneous microstructure. Tensile tests showed that this alloy exhibited a superior combination of high yield strength (692 MPa), high tensile strength (1115 MPa), high work hardening rate and large uniform elongation (33.5%). More importantly, the new technique proposed in this work could be potentially applicable to other alloy systems with segregation problems.

Improving the production efficiency of high-titania slag in Ti extraction process: fluxing effect on formation of pseudobrookite

“…The experimental temperature was 1873 K and was controlled within ±2 K using a B-type (Pt-30%Rh/ Pt-6%Rh) thermocouple and a proportional integral differential controller. After the temperature stabilized, a mixture of ilmenite ore and flux (100 g) was quickly added onto the surface of the pre-melted iron bath and maintained for 1 h. Slag samples were collected at defined time intervals (5,7,10,15,20,30 and 60 min) using a steel rod dipped into the slag layer. The samples were quenched rapidly by flushing with high-purity (99.999%) Ar gas (flow rate of 25 L/min).…”

Microstructure, phase composition and mechanical properties of new, low cost Ti-Mn-Nb alloys for biomedical applications

“…3 with high melting points and high densities such as Ti-70Ta, Ti-29Nb-13Ta-4.6Zr and Ti-42Nb [12][13][14]. The high melting points of these alloying elements introduces increased difficulty to the processing of biocompatible Ti alloys and make the alloys more prone to compositional segregation which is detrimental to their mechanical properties and performance [15,16]. Additional post-fabrication processes such as high temperature homogenising heat treatments and/or thermoplastic processing are required to alleviate or eliminate segregation [16] which adds to their expense.…”

“…The high melting points of these alloying elements introduces increased difficulty to the processing of biocompatible Ti alloys and make the alloys more prone to compositional segregation which is detrimental to their mechanical properties and performance [15,16]. Additional post-fabrication processes such as high temperature homogenising heat treatments and/or thermoplastic processing are required to alleviate or eliminate segregation [16] which adds to their expense. Therefore, due to the high content of costly alloying elements and difficulty in alloy fabrication, many of the recently developed Ti alloys are not competitive with current commercial Ti alloys [15].…”

The Effect of Heating Rate on Discontinuous Grain Boundary Alpha Formation in a Metastable Beta Titanium Alloy

“…The suppression of continuous a GB is crucial to achieve both high strength and high ductility, especially in precipitation-strengthened metastable b titanium alloys. [21][22][23][24] However, similar to a+b titanium alloys, [22,31] the preferential nucleation and growth of a phase at b grain boundaries during aging makes it difficult to avoid. [22] The most efficient route to alleviate the a GB formation is wrought processing, [32] but this route is not applicable to the promising near-net-shape processing methods, such as additive manufacturing.…”