Accession Number:

ADA169747

Title:

Fundamental Investigations of Failure during Superplastic Forming Process

Descriptive Note:

Final rept. 1 Feb 1982-31 Jan 1986

Corporate Author:

CALIFORNIA UNIV DAVIS DEPT OF MECHANICAL ENGINEERING

Personal Author(s):

Report Date:

1986-04-01

Pagination or Media Count:

101.0

Abstract:

The experimental work on both the base alpha-beta alloy Ti-6Al-4V and the Ni-modified alloy Ti-6Al-4V-2Ni showed that there is significant microstructural evolution during superplastic deformation. These structural evolutions affect the parameters for the constitutive equation for superplasticity. Contrary to model prediction, the strain rate sensitivity is found to be a function of temperature, in a way that exactly parallels the dependence of beta-volume fraction on temperature. An empirical equation has been proposed to characterize the non-steady state microstructure in terms of the dependence of strain hardening coefficient on temperature and strain rate. The maximum attainable ductility in this alloy is associated with a dynamic balance between strain hardening due to grain growth and strain softening due to in situ grain refinement. The 7475-TR6 aluminum alloy heat B undergoes significant level of strain hardening due to increase in dislocation density as a function of strain. The grains do not remain equiaxed which is contrary to most supposition of superplasticity. One does not observe a true steady-state in the microstructure during superplastic deformation. The activation energy of deformation is equal to that for volume diffusion, possibly due to the necessity of the dislocations to climb over the Cr-rich particles. The alloy cavitates extensively due to decohesion of the intermetallic particlegrain boundary interface.

Subject Categories:

  • Properties of Metals and Alloys
  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE