Compositional Optimization of β Type Titanium Alloys with Shape Memory Ability and Their Characteristics

Abstract

The compositions of ¢ type Ti alloys having shape-memory ability above 400 K were proposed by alloying parameters used in the delectrons concept. They were both Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo which were designed for improvement of thermal stability in shape memory behavior of Ti-6Mo base alloy, preserving the tensile strength of 700 MPa. Their ingots without contamination from the used crucible were produced by cold crucible levitation melting. They consisted of ¢ and ¡AA phases after the cold roll and heat treatment, and their amounts were depended on values in the alloying parameters. The shape recovery rate of 40 and 25% was measured after 4 cycles in the loadingunloading tests in Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo, respectively. They showed the As temperature above 490 K and improvement of thermal stability because of a much smaller amount of ½ phase than Ti-6Mo. The alloys showed tensile strength of 682 to 718 MPa. These results were caused by exactly prediction of the phase stability, shape memory ability and tensile strength, using alloying parameters.

Achievement of Room Temperature Superelasticity in Ti-Mo-Al Alloy System via Manipulation of ω Phase Stability

“…About 1/3 residual strain (i.e., 0.8%) of shape recovery took place upon heating due to SME (ε sme ). These results agreed well with Ti-6 mol% Mo and Ti-11 mass% Mo (= Ti-5.81 mol% Mo) alloys [23,24]. Additionally, Ti-11 mass% Mo alloy possessing proximate composition to 0Al was reported to undergo plastic deformation mainly by twinning deformation of the β phase [25,26] and was accompanied by SIMT simultaneously in the early stage [27][28][29][30].…”

Possibility of As-Cast Applications on β-Type Titanium Alloys Proposed in the Newly Expanded Area of <i>Bo_t-Md_t</i> Diagram

“…The different grain sizes of alloys were obtained by both cooling methods of molten metals, that is, the solidification in the melting copper (Cu) crucible and split-cold mold placed below the hole of the melting Cu crucible in the bottom part of the melting furnance. 9,31) In contrast, the different grain sizes could also be influenced by the different Ar gas purity. 31) These Ti ingots were prepared in the solidification of the melting Cu crucible under the purity of 99.99% Ar atmosphere in the present study.…”

“…16,17) The d-electrons concept based on the theoretical calculation of electronic structure theory has been applied to the design of high-performance materials such as Al, Bi, Ni, Zn, and Ti-based alloys. 9,1822) Two calculated parameters are utilized in the d-electrons concept, the bond order (Bo), which is a measure of the covalent bond strength between Ti and an alloying element, and the d-orbital energy level (Md), which correlates the electronegativity and metallic radius of elements. 23,24) The d-electrons concept is easy and convenient to use in practical applications, compared with other alloy design methods such as the phase-field method and the thermodynamic modeling of ordered phases.…”

“…2830) These elements and other impurities are usually derived from the gas environment of the furnace and the contaminations of the crucible in the process of melting. 9,17,31) The choice of appropriate melting equipment is essential for the preparation of Ti alloys. Cold crucible levitation melting (CCLM) consists of a highfrequency induction furnace and two electric coils.…”

Design of Near α-Ti Alloys with Optimized Mechanical and Corrosion Properties and Their Characterizations

“…The molten metals were raised by the eddy current of CCLM and were melted without contact with the crucible. An even distribution of solute elements in Ti alloys was attained by diffusion mixing and the strong stirring induced by electromagnetic forces, and the solidification cooling processes for molten alloys could be controlled by CCLM [13][14][15].…”