Hiroaki Kurishita

The high temperature deformation mechanism in titanium carbide single crystals

In order to investigate the high temperature deformation mechanism in titanium carbide, single crystals were grown by the r.f. floating zone technique and were deformed by compression at temperatures from 1280 to 2273 K and at strain rates from 3.9 × 10−5 to 6.3 × 10−3s−1. The crystals exhibited a marked work-softening phenomenon which is characteristic of covalently bonded crystals such as germanium and silicon, and the phenomenon became less clear with increasing temperature and with decreasing strain rate. The mechanical equation of state at the yield stress can be expressed by nλ> = AτcGmexp−QRT nwhere m = 10 andQ = 240 kJmol− in the low temperature range at and below 1510 K and where m = 5.3 andQ = 470 kJmol−1 in the high temperature range at and above 1840 K. It is considered that the deformation in the low temperature range is controlled by the Peierls mechanism and the deformation in the high temperature range by the diffusion of carbon atoms.

Determination of high-temperature deformation mechanism in crystalline materials by the strain-rate change test

Abstract A new method is proposed to determine whether the effective stress for the viscous or quasi-viscous motion of dislocations exists or not in the deformation of crystalline materials. The crosshead speed is changed on the way of deformation and the work-hardening rate is measured immediately after the change. It is theoretically predicted that the work-hardening rate depends on whether the effective stress is negligible or not. Applying the method to high-temperature deformation of pure aluminum and Al-5.4 at.% Mg alloy, it is found that the effective stress is negligible in pure aluminum at all temperatures tested and in the alloy at temperatures where the dynamic strain aging occurs, while the stress is appreciable in the alloy at temperatures where the solute atmosphere dragging occurs.

The high temperature deformation mechanism in pure metals

Abstract In order to demonstrate that the high temperature deformation of f.c.c. and b.c.c. pure metals is controlled not by a glide process but by a recovery process, a thorough examination of distinctions between the two controlling mechanisms in issue is made, in particular in view of the effect of an experimental error involved in the strain rate change test. It is shown theoretically that the effect of the error behaves in a different manner corresponding to the two mechanisms and, in turn, the different behaviour provides an improved analysis to determine the high temperature deformation mechanism. It is presented that the result obtained by the application of the analysis to the high temperature deformation of pure Al and the other deformation characteristics of f.c.c. and b.c.c. pure metals reported so far are well explained by the recovery controlled process, in agreement with the authors previous conclusion.

High-temperature deformation mechanism in substoichiometric titanium carbide - correlation with carbon vacancy ordering

In order to clarify the reason for the marked nonstoichiometry-effect on the mechanical properties of TiCx, the order structure has been investigated in a wide range of CTi atom ratios, x, from 0.59 to 0.95 by the transmission electron microscopy. n nIt is found that the as-grown crystals are weakly or strongly short-range ordered (SRO) depending on x and have a long-range ordered structure (LRO) at x = 0.59 at room temperature. As temperature rises, the degree of order tends to decrease, and around 1300 K, where a marked x-effect on mechanical properties was observed, the diffuse electron scattering due to SRO becomes very weak for x > 0.85, but still strong for x = 0.75, and there exist micro domains of LRO for x = 0.59. From the order structure and the additional experiment of aging effect on the initial deformation behaviour, it is concluded that the x-dependence of deformation behaviour can be understood as an ordering effect of carbon vacancies.

Chemical states of oxygen segregated intergranular fracture surfaces of molybdenum

Abstract The Auger and electron energy loss spectra (EELS) of a grain boundary fracture plane of bicrystal molybdenum (32 wt.ppm oxygen) are compared with the spectra of pure and oxidized molybdenum. The Auger spectrum of the fracture surface contains molybdenum and oxygen peaks, and the Mo M 4,5 NN line coincides with that of the pure metal. The interfacial Auger transition peak is observed on the low energy side of the Mo N 2,3 VV Auger peak. Both AES and EELS spectra of the fracture plane are different from those of the oxidized molydenum. These results show that the segregated oxygen is bound to the grain boundary fracture plane as if it were adsorbed.

Dislocation Motion in FCC Metal Crystals

ABSTRACT Motion of dislocations in well-annealed and neutron-irradiated copper single crystals has been studied using an etch-pit technique and microcinematography. At pre-yield deformation of well-annealed Cu, individual dislocations with edge nature generally move much larger distance than those with screw nature. In stage I of neutron-irradiated Cu the average velocity of edge dislocations moving in slip bands is larger than that of screw ones. It is concluded that (i) slow motion of screw dislocations in well-annealed Cu comes from as-grown jogs and low velocity of screw ones in neutron-irradiated Cu comes from jogs produced along them during deformation dislocations and from cross-slip, (ii) slip bands of neutron-irradiated Cu grow in width and length by successively forming dislocation sources on adjacent slip planes (relay-race mechanism).

Surface effect in yielding and stage I deformation of neutron-irradiated copper crystals

Abstract In order to make clear the inhomogeneity of plastic deformation of neutron-irradiated copper crystals, detailed observation of primary and secondary slip band and precise examination of lattice rotation have been carried out in yielding and stage I deformation using an etch-pit technique and a precise Laue method. Main results are as follows: (i) a free surface plays an important role for the multiplication of primary and secondary dislocations, and (ii) secondary slips contribute to the completion of plastic bending of a crystal due to the constraint of grips and the heterogeneity of deformation.