Improvement of high cycle fatigue strength of P/M Ti-6Al-2Sn-4Zr-2Mo/TiB particulate composites by the modification of matrix microstructure

摘要

The present authors have previously shown that in the Ti 6A1 2Sn-4Zr-2Mo/10TiB particulate composites the fatigue fracture originated neither from the interior of particulate nor from theparticulate matrix interface, but rather from the matrix area of the composites. This finding strongly suggested that the high cycle fatigue strength is related with the matrix microstructure. Therefore,the present study aimed at improving the high cycle fatigue strength by the modification of matrixmicrostructure.The Ti-6Al-2Sn-4Zr-2Mo/10TiB particulate composites were produced by the blendedelemental P/M method using extra low chlorine titanium powder smaller than 45 μm in diameter.The smooth axial fatigue tests were carried out at an R ratio of 0.1 in the load-controlled mode.The matrix microstructure was highly dependent on the cooling rate after the sintering treatment.The faster cooling rate of 10K/sec produced the well-defined colony microstructure. The massivecolony microstructure was obtained by the cooling rate slower than 0.3K sec. The modification of the matrix microstructure from a colony into a fine acicularα microstructure resulted in the increase in high cycle fatigue strength. For example, fatiguestrength at 10{sup}7 cycles was increased from 490 MPa to 550 MPa. The three main contributions to the fatigue strength were suggested as the contribution from the increase in Young's modulus (18%), tensile strength (39%) and microstructuralmodification (43%), respectively.