An x-ray diffraction study of consolidation processes in the rolling of nickel powders

Abstract

1. As a result of an investigation into the compressibility of nickel powders in strip rolling, it was established that the best compressibility over the range Psp max = 12.5–67 kN/cm2 (1.25–6.7 tons/cm2) is exhibited by atomized powder and the poorest compressibility by carbonyl-nickel powder. The relationships established are supported by results of x-ray diffraction studies. 2. Using x-ray diffraction techniques, it was determined that the broadening of the interference lines of carbonyl-nickel specimens is linked with the size of c.s.r., the magnitude of microdistortions, and the presence of s.f. The role of each factor depends on the degree of compression of the powder: For the starting powder, the extent of broadening due to s.f. amounts to about 30% of the physical breadth of the (111) line. After rolling at Psp. max = 67 kN/cm2 (6.7 tons/cm2), the line-breadth fraction due to s.f. decreases by half. 3. The presence of s.f. in the starting carbonyl nickel and in strips rolled from it confirms that the crystal-growth and plastic-deformation processes are governed by the dislocation mechanism. 4. The relationship MΔa/a- 0.4d, obtained for cold-deformed bulk nickel, has been found to apply also to the rolling of carbonyl-nickel powder over the range Psp. max = 46–67 kN/cm2(4.6–6.7 tons/cm2).