Papers by Author: Yonosuke Murayama

Abstract: Metastable beta Ti-Cr-Sn-Zr alloys used as biomaterial show low Young’s modulus and super-elasticity according to the phase stability of their beta phase. In this study, we substituted Nb and Fe for Cr in metastable beta Ti-2Cr-6Sn-45Zr alloy and investigated their effect. We investigated how the added amount of Cr, Nb and Fe influences the phase stability and the properties of low Young’s modulus and super-elasticity in Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloys. The Young’s modulus of a Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy decreases with the addition of Cr, Nb or Fe. However, the Young’s modulus of a Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy increases with the addition of Cr, Nb or Fe after showing own minimum value respectively. Minimum Young’s modulus of several Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloys were under 50GPa. The required amount of Cr, Nb or Fe in the Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy having minimum Young’s modulus is different according to the beta stabilizing ability of each element. Fe amounts were the smallest and Nb amounts were the largest. Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy with minimum Young’s modulus shows a stress-induced martensitic transformation. However, only Ti-Cr-Sn-Zr alloys showed definite super-elasticity. The recovered strain by super-elasticity is small in Ti-Nb-Sn-Zr alloy. Ti-Fe-Sn-Zr alloy didn’t show super-elasticity or large elongation.

Abstract: The Young’s modulus of Ti-Cr-Sn-Zr alloy varies with the composition of Cr, Sn and Zr, in which the elements act as β stabilizers. Some Ti-Cr-Sn-Zr alloys show very low Young’s modulus under 50GPa. The amount of Zr in alloys with very low Young's modulus increases with the decrease of Cr. We investigated the Young’s modulus and deformation behavior of Ti-xCr-Sn-Zr (x=0~1mass%) alloys containing a large amount of Zr. The quenched microstructure of Ti-Cr-Sn-Zr alloys changes from martensitic structure to β single-phase structure if the amounts of β stabilized elements are increased. The Ti-Cr-Sn-Zr alloys with compositions close to the transitional composition of microstructure from martensite to β phase show minimum Young’s modulus. The clear microstructural transition disappears and the minimum Young’s modulus increases if the amount of Cr becomes too small. In Ti-Cr-Sn-Zr alloys containing a large amount of Zr, Young’s modulus depends on β phase that is intermingled with martensite.

Abstract: This work investigates the mechanical properties of Ti-Cr-Sn-Zr alloys containing large amount of Zr. We focuses on the effect of the varying alloy composition on the microstructure, the Young’s modulus, the deformation mechanism and the deformation behavior. Ti-Cr-Sn-Zr alloys show much low Young’s modulus in the narrow composition range for Cr but wide for Zr. The Young’s modulus of Ti-2Cr-6Sn-xZr (x=5~60mass%) alloy decreases with increasing Zr and shows the minimum value of 41GPa in Ti-2Cr-6Sn-45Zr alloy. The alloys with low Young’s modulus consist in meta-stable β phase. The composition of the meta-stable β phase is close to the transition where the quenched microstructure transits from martensite to meta-stable β phase. Ti-2Cr-6Sn-45Zr alloy with lowest Young’s modulus show the super-elastic property.

Abstract: This work investigates the mechanical properties of Ti-Cr system alloys and focuses on the microstructure, the Young’s modulus, the deformation mechanism and the deformation behaviour observed in various alloy compositions. The addition of Al to the Ti-Cr system alloys greatly decreases the Young’s modulus. Addition of Al, Sn and Zr to various Ti-Cr alloys suppresses the athermal ω phase that forms during quenching from β field. A Ti-Cr system alloy with low Young’s modulus was obtained in suitable compositional combination of Cr, Zr and Sn or Al. The alloys with the composition where the quenched microstructure transits from martensite to meta-stable β phase show low Young’s modulus. In addition, the alloys show two-step yielding due to stress-induced transformation.

Abstract: Low modulus β Ti alloys are attractive for biomedical application. This work examines the mechanical properties of Ti-Cr-Sn-Zr system alloys, especially the effect of the varying alloy composition on the microstructure, the Young’s modulus and the deformation mechanism.The Young’s modulus of the alloy varies with the composition, which variation is caused mainly from the competition between the meta-stable β phase and ω phase.The deformation modes of the Ti-Cr-Sn-Zr alloy, which are the mechanical twinning, the deformation by slip and the deformation-induced transformation, also change depending on the composition of the alloy. The minimum of the Young’s modulusof the Ti-Cr-Sn-Zr alloy in this experiment was shown in the composition where the microstructure of the alloy changes from the martensitic structure to the meta-stable β structure.

Abstract: A2O3/YAG/ZrO2 eutectic Melt-Growth-Composites (MGCs) were unidirectionally solidified by the modified-pulling-down method (MPD) and the Bridgman type method, in which a crucible was brought down at different speeds. The microstructures and crystallographic textures were studied by field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The high-temperature strength was investigated by compression tests. All MGC rods show strong preferred growing orientation, although the structural size of eutectic microstructure among MGC rods was different. The high-temperature strength of MGC rods is dependent on orientation, compression temperature and strain rate. The high-temperature strength of MGC rods is controlled by the anisotropic strength of constituent Al2O3, as well as the structural size of eutectic microstructure.