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I.

INTRODUCTION

A recent publication has dealt extensively with the plastic deformation of polycrystalline Nb3Sn.1 Deformation was observed over a strain rate range from 10-6 to 10-2 per second and over a temperature range from 1150 to 1650 ~ Throughout most of these ranges, load-relaxation test stress-strain rate relationships were consistent with "power law creep", and the mechanical data suggested an activation energy for creep of roughly 500 kJ/mol. Plastic deformation was observed in simple compression testing at 1400 ~ and above, with brittle intergranular fracture occurring at 1400 ~ and with ductile, void-growth-related fracture occurring at higher temperatures. Several previous papers have reported plastic deformation of A 15 compounds, both at room temperature 2-5 (under high hydrostatic pressure) and at elevated temperature 6'7'8 (under ambient pressure). Single crystal studies of V3Si have noted {100} (010) slip behavior, 7'8 and dislocations with cube direction Burgers vectors have been observed. 9 Hot deformed microstructures have displayed polygonized dislocation structures) ~ Deformation processing of A15 compounds has been considered by one of the authors.12 The effect of grain size on A15 plastic deformation has not been rigorously considered. The previous work on polycrystalline NbaSn I involved 60 p.m grain size specimens that had been prepared from elemental powder by hot isostatic pressing (HIP) at 1630 ~ The 60/zm grain size was stable during testing. A few mechanical tests were performed on 12/xm grain size material hot isostatically pressed at 1200 ~ However, this material underwent grain growth at test temperatures above 1200 ~ and no rigorous grain size effect evaluation was possible. The present paper concerns an evaluation of Nb3Sn over a grain size range of 10 JAMES B. CLARK is Graduate Assistant, The Johns Hopkins University, Baltimore, MD 21218; GEORGE B. HOPPLE is Materials and Processes Engineer, Lockheed Missiles and Space Division, Palo Alto, CA 94302; and ROGER N. WRIGHT is Associate Professor, Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12181. Manuscript submitted February 28, 1982. METALLURGICALTRANSACTIONSA

to 60/xm, involving material that is microstructurally stable in the 1150 to 1650 ~ range. The relatively fine, stable grain size was achieved by doping with Zr to form a fine ZrO2 dispersion, after Benz.13

II.

MATERIAL PREPARATION

Bulk samples of Nb3Sn were prepared by hot isostatic pressing blends of Sn and Nb powder and blends of Sn and Nb- 1 pct Zr powder. The Sn powder was AMAX TF- 1, with a purity of 99.99 pct. The Nb and Nb-1 pct Zr powders were obtained from Teledyne Wah Chang. The chemical analyses of the Nb and Nb-1 pct Zr powders are given in Table I. The particle size distributions of the Nb and Nb1 pct Zr powders were determined with a Roller air analyzer (ASTM standard B-293-60), and the distributions are given in Table II. The powder blending involving Nb powder incorporated 70.1 pct wt pct Nb powder and 29.9 wt pct Sn