Texture strengthening in high-temperature applications such as heat-exchanger materials

CIM Bulletin, Vol. 74, No. 831, 1981

S. SAIMOTO, L COLLINS and G.B. HOBBS, Queen's University, Department of Metallurgical Engineering Kingston, Ontario

Plastic yielding and flow in metals is dependent on the microscopic process of simple shear along crystallographic planes and directions known as slip. Thus, by altering the crystallographic direction of the stress axis or placing constraints in the direction of plastic flow, anisotropy of yield strength for the same material is observed. This phenomenon is called texture strengthening. The application of this concept to highly anisotropic crystal structures such as the hexagonal group of titanium and zirconium alloys, the former in missile casing and the latter in nuclear reactor fuel tubing, seems obvious. The outstanding example in cubic structures is the case of deep-drawing steel. The R value, the width strain over the thickness strain during a tensile test, is taken as a measure of texture strengthening. In face-centred cubic structures, texture strengthening has been completely ignored on the basis that materials with R less than one are not amenable to this beneficiation. This study will review two aspects of texture which will lead to strengthening, first the thermal stability of the deformed microstructure, which is dependent on the stress axis, and second, the texture strengthening aspect of fee metals.A review of recovery and recrystallization in textured aluminum wires, copper and cupro-nickel sheet will be presented with the view of extending these concepts to the manufacture of heat-exchanger tubing. The superior creep properties of specially processed commercial products such as TD-Ni, TD-NiCr and MAR-M200 will be shown to be a manifestation of the same physical phenomena.

Keywords: Technology, Metallurgical sciences, Strengthening, Texture strengthening, Heat exchangers, Shear, Stress, Plastic flow, Yield strength, Alloys, Titanium alloys, Zirconium alloys, Copper sheet, Cupro-nickel sheet, Aluminum wire, Steel.