Strength and creep of structural materials based on intermetallic compound NiAl

Abstract

The effect of thin tungsten and molybdenum layers, which were applied onto powder particles of intermetallic compound NiAl or its alloys with Hf and Nb before their pressing, on the hot strength and short-time creep strength of compact samples obtained from such granules has been studied. Such materials are proposed to be called composite materials (CM) with a honeycomb structure. Miniature samples in the form of small cylinders 5 mm in diameter and 5–8 mm in height were tested for compression at 1000–1300°C in air and for creep upon compression at 1050, 1110 and 1210°C in a vacuum. Alloying NiAl with hafnium or niobium increases the hot strength of the alloys by a factor of 1.4–3.7; the formation of honeycomb structure increases this characteristic by a factor of 1.6–3.6 at 1000°C; with increasing test temperature to 1300°C, the effect of solid-solution strengthening decreases to values typical of pure NiAl (σy = 7–12 MPa), and the effect of the honeycomb structures increases to σyCM / σyNiAl 6–7 at σyCM = 50–80 MPa. The creep strength characteristics of the CM σ1%h/y and σ10%h/y at all test temperatures are higher by a factor of 1.5–2.4 than those of NiAl and its alloy with Hf; they are as high as σ1%h/1210 = 40.4 MPa and σ10%h/1210 = 61.3 MPa for the NiAl + W(1 μm) CM and σ1%h/1210 = 17.7 MPa and σ10%h/1210 = 26.3 MPa for NiAl. For the composite material with a honeycomb structure, the attained gain in the working temperature relative that of the nonstrengthened NiAl is ∼ 160 K.