THE STRUCTURE AND MECHANICAL PROPERTIES OF Ti/TiAl₃  MICROLAYER MATERIALS PRODUCED BY ROLLING AT VARIOUS TEMPERATURES

Abstract

Three Ti/TiAl₃ microlayer titanium materials, produced by sintering and rolling of alternating titanium and aluminum strips of different thickness at 600, 700, and 770° C, were developed and studied. To prevent oxidation in the sintering and hot rolling processes, an argon-arc-welded stainless-steel container that contained a layered workpiece was used for all materials. After hot rolling (one pass), cold rolling was performed to strengthen the titanium bearing layers and reduce the shear strength of the intermetallic layer resulting from reaction of titanium with aluminum in sintering. The initial thickness of the titanium and aluminum layers was 220 and 50 μm in one case and 100 and 10 μm in the other. The structure of sections and fatigue fractures of the materials was analyzed using photos taken with a scanning electron microscope. The thicknesses of the titanium layers varied from 15 to 28 μm and that of the intermetallic layers from 10 to 22 μm. Fatigue failure of structural elements in the materials was examined. The intermetallic layer failed by shear in the middle of its thickness. The fractured surface of the samples had steps of approximately the same length and depth. The intermetallic particles had both equilibrium shape with an average diameter of 2–3 μm and lamellar shape with a thickness of 0.5–1 μm and a length of 3–5 μm. Tests of samples with a thickness of 0.25 to 0.5 mm for three-point bending under static load at room temperature showed that their limit of proportionality reached 710 MPa and the total strain to failure was 2.7%. The load diagram showed a monotonic increase in the load of the samples to the maximum and then stepwise decrease and increase in load associated with subsequent failure of the bearing titanium layers and shear of the intermetallic layers around the failed bearing layers. This resulted in a substantial area under the load diagram, corresponding to the fracture energy of the material.