The Behavior of Intermetallic Compounds at Large Plastic Strains
- PDF / 341,730 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 34 Downloads / 208 Views
THE BEHAVIOR OF INTERMETALLIC COMPOUNDS AT LARGE PLASTIC STRAINS 9EORGE T. GRAY III* AND J. DAVID EMBURY** AlamosUniversity, National Laboratory, Los Alamos, New Mexico 87545 **Los McMaster Materials Science Department, Hamilton, Canada. ABSTRACT Much effort has been devoted to the study of ordered materials at modest plastic strains and the problem of premature failure. However by utilizing stress states other than simple tension it is possible to study the deformation of intermetallic compounds up to large plastic strains and to consider the behavior of these materials in the regime where stresses approach the theoretical stress. The current work outlines studies of the work hardening rate of a number of titanium and nickel-based intermetallic compounds deformed in compression. Attention is given to the structural basis of the sustained work hardening. The large strain plasticity of these materials is summarized in a series of diagrams. Fracture in these materials in compression occurs via catastrophic shear at stresses of the order of E/80 (where E is the elastic modulus).
Introduction Much effort has been devoted to the elucidation of detailed dislocation configurations in a variety of ordered compounds and to the temperature dependence of the flow stress. However to date little attention has been paid to the behavior of these materials at large plastic strains. In large part this reflects the limited ductility of many of these compounds in tension. In the current work we have considered the plasticity of ordered intermetallics in terms of their response to compressive deformation. The objective of this work can be summarized by considering the deformation history in the following sequence of events. a) How do intermetallics differ from pure metals in terms of their ability to sustain work hardening? b) What stress levels can be attained in intermetallic compounds after large strains and what configurations of lattice defects are required to attain these stress levels? c) At large plastic strains what are the essential competitive processes between continuing plasticity and fracture? Clearly in the limitations of a conference paper only a basic outline of these aspects can be covered. This paper contains a summary of a broad study of intermetallics which includes the following materials, Ni3Al, Ti-48AI-lV, Ti-24AI-llNb, Ti-48AI-2Cr-2Nb, and Ti-24.5AI10.5Nb-l.5Mo. Experimental Procedure An experimental program was conducted to examine the deformation and work-hardening response of a number of Ti-aluminides and Ni3AI deformed to large strains in compression. The essential microstructural features and initial yield stresses of these materials are summarized in Table I. The quasi-static stress-strain response of the materials was measured using an Instron machine for strain rates in the range 10- 3 to 0.1 s-1. The dynamic constitutive response, strain rates of 1000 to 8000 s-1, was measured with a Split-Hopkinson pressure bar. Testing to large true strains was accomplished using repeated reloading of samples with
Data Loading...
