Effect of silicide precipitation on tensile properties and fracture of alloy Ti-6Al-5Zr-0.5Mo-0.25Si

The effect of silicon in solid solution and in the form of suicides has been studied on the tensile properties and fracture behavior of alloy Ti-6Al-5Zr-0.5Mo-0.25Si (alloy 685). The heat treatment to hold silicon in solid solution consists of solutionizing at 1323 K for 0.5 hour under vacuum (∼10^-5 MPa), followed by water quenching, and the treatment to precipitate suicides involves subsequent aging of the solutionized and water quenched specimens at 1073 K for 24 hours. There is only marginal effect of the aging treatment on strength values; however, the ductility parameters are found to be drastically reduced. There are marked differences in the fracture behavior of the alloy in the as-quenched and the quenched and aged conditions. While the fracture surface of the unaged specimen shows characteristic dimples, there is a large number of facets on the fracture surface of the aged specimen. The facets in the central region are relatively smaller in size than those in the peripheral zone. The central facets show fluted features at higher magnifications; however, the peripheral facets are usually featureless. The faceted fracture in the aged condition is attributed to enhanced tendency for heterogeneous planar slip. The fracture characteristics correlate with the observed differences in the ductility in the two conditions.     

Influence of hold time on low cycle fatigue behaviour of near alpha titanium alloy IMI 834 at 873K

In the present work, IMI 834, a near α titanium alloy was evaluated for tensile and low cycle fatigue (LCF, with and without hold time) behavior at 873K. Tensile tests were performed at the initial strain rate of 4 × 10^?3 s^?1 at 873K. Fully reversed, total strain control LCF tests were conducted at total strain amplitude of ± 1.0% at constant strain rate of 4 × 10^?3 s^?1 at 873K. For LCF tests with dwell, hold time were imposed in tension, compression and tension — compression mode with varied hold times of 60 sec, 120 sec, 180 secs. In LCF tests without dwell, the Coffin-Manson plot showed dual slope behavior at 873K. In LCF tests with dwell, at 873K, tensile, compressive and tensile — compressive hold time tests have shown lower LCF resistance than that of the tests without hold time. Among the three modes of hold times employed, the tensile hold has exhibited the highest LCF resistance followed by tensile — compressive and compressive hold time tests. In the present study, tensile hold introduces compressive mean stresses while the compressive hold introduces tensile mean stresses. Further, the creep effect of stress relaxation was examined at 873K in order to explain the hold time effects.     

Fatigue Crack Growth Behaviour of Conventional and Modified IN 718 Superalloys at 650 °C

In the present investigation, the fatigue crack growth behaviour of modified IN 718 superalloy (Ni-0.02 %, C-19.04 %, Cr-19.31 %, Fe-3.04 %, Mo-4.73 %, Nb-1.01 %, Al-1.16 %, Ti-0.0033 %, B, all in wt%) has been compared with conventional IN 718 superalloy (Ni-0.02 %, C-19.0 %, Cr-19.35 %, Fe-3.0 %, Mo-5.10 %, Nb-0.50 %, Al-1.00 %, Ti-0.0033 %, B, all in wt%) at 650 °C. Modified IN 718 superalloy exhibits marginally lower crack growth rate as compared to conventional alloy and was attributed to roughness induced crack closure.