Microstructure and Mechanical Properties of Ti-Nb Alloys Prepared by Mechanical Alloying and Spark Plasma Sintering

Abstract

The effect of Nb content on microstructure, mechanical properties and superelasticity was studied in Ti-Nb alloys fabricated by powder metallurgy route using mechanical alloying and spark plasma sintering. In the microstructure of the as-sintered materials, undissolved Nb particles as well as precipitations of a-phase at grain boundaries of b-grains were observed. In order to improve the homogeneity of the materials, additional heat treatment at 1250°C for 24 h was performed. As a result, Nb particles were dissolved in the matrix and the amount of a-phase was reduced to 0.5 vol.%. Yield strength of the as-sintered alloys decreased with Nb content from 949 MPa for Ti-14Nb to 656 MPa for Ti-26Nb, as a result of the decreasing amount of a-phase precipitations. Heat treatment did not have a significant effect on mechanical properties of the alloys. A maximum recoverable strain of 3% was obtained for heat-treated Ti-14Nb, for which A s and A f temperatures were 2 12.4 and 2.2°C, respectively.

Superelastic Behavior of Ti-Nb Alloys Obtained by the Laser Engineered Net Shaping (LENS) Technique

“…This value was associated mainly with the R E part, as a result of the low elastic modulus (25 GPa) and high YS (above 1000 MPa). In our previous work [ 12 ], we also showed 3% of recoverable strain for sintered Ti-14Nb alloy, however, this value was related mainly to the R E part because of the high YS (920 MPa) of the alloy.…”

“…The found orientation relationship was . Although the ω phase is metastable under ambient conditions, it is typically observed in Ti-Nb alloys in the form of nanometric precipitations uniformly distributed in the matrix [ 12 , 36 , 37 ]. The presence of these precipitations mechanically suppresses the martensitic transformation, but, on the other hand, it increases the critical stress for slip deformation which is low for single-phase Ti-Nb alloys [ 2 ].…”

“…In addition, porous or cellular structures can be manufactured, which is difficult or even impossible using casting techniques [ 10 , 11 ]. In our previous work [ 12 ], we showed that Ti-Nb alloys obtained using mechanical alloying (MA) and spark plasma sintering (SPS) possess a much higher strength in comparison to cast alloys; e.g., the yield strength (YS) of the cast and solution-treated Ti-26Nb alloy reaches about 300 MPa, while, typically, for alloys obtained using the PM route, it exceeds 700 MPa [ 12 , 13 ]. The hardening effect in PM Ti-Nb alloys may be attributed mainly to the effect of interstitial contamination, e.g., oxygen.…”

Effect of Mo and Ta on the Mechanical and Superelastic Properties of Ti-Nb Alloys Prepared by Mechanical Alloying and Spark Plasma Sintering

“…Due to a wear process that take place during the milling, the WC phase was introduced to the particles. As described in our previous work [ 18 ] the amount of the carbides increases with the increasing milling time, therefore the intermediate synthesis time of 30 h was selected in order to avoid the extensive contamination and to obtain a satisfactory level of the mixing of the elemental powders.…”

“…Consequently, the superelastic properties were observed in sintered Ti-13Nb and Ti-11Nb alloys containing 2.5 and 4.0 at.% of oxygen, respectively [ 16 , 17 ]. Similarly, our previous studies on the spark-plasma sintered Ti-Nb alloys, showed that in order to obtain the superelastic properties, the concentration of Nb has to be reduced from the initial 26 to 14 at.% [ 18 ].…”