Neutron diffraction study of thermal residual strain in three layered materials made by self-propagating high-temperature synthesis

The thermal residual strain in the three layered materials, [WC-10mass%Ni]-[Ni]-[WC-10mass%Ni], [WC-10mass%Ni]-[SUS304(plate)]-[WC-10mass%Ni] and [WC-10mass%Ni]-[Ni(plate)]-[WC-10mass%Ni], has been investigated by neutron diffraction measurement. They were made by self-propagating high-temperature synthesis. Original materials of composite [WC-10mass%Ni] are powders of W, C and Ni, and those of the middle layers are the powders of Ni, a plate of SUS304 and a plate of Ni. The samples were 40mm in diameter and about 4mm in thickness of each layer. The result of the measurement shows that the middle layer made from powders of Ni has no strain, which suggests that it shrinks from high temperature freely from the existence of both side layers. On the other hand, the middle layer made from a plate material experiences complex stress according to each position and to each direction of the sample, which suggests that it shrinks from high temperature in a state of tight binding on both side layers. The Ni region in the composite material, [WC-10mass%Ni], has a large tensile strain of 0.6 to 1.0%, whereas WC region has a negligibly small compressive strain. In this case, the Ni region shrinks under the hard connection with the WC region, of which the thermal expansion coefficient is relatively small.