High temperature deformation behavior of titanium samples with superplastic layer
- PDF / 4,609,839 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 84 Downloads / 194 Views
R. Z. Valiev Department of Materials Science, Ufa State Technical University, Ufa 450025, Russia
P. Lukac Department of Metal Physics, University, Ke Karlovu 5, 121 16 Prague-2, Czech Republic
A. K. Mukherjee Department of Chemical Engineering and Materials Science, University of California, Davis Davis, California 95616-5294 (Received 17 August 1994; accepted 28 November 1994)
The progress of high temperature deformation in samples of two commercial titanium alloys with superplastic (SP) structure, non-SP structure, and with an SP layer sandwiched between the non-SP regions has been studied on the scale of the entire deformed volume and on the scale of grain groups. The results of mechanical behavior showed that samples with SP layer exhibit higher stress level than those with completely SP structure and higher strain rate sensitivity than those with completely non-SP structure. Samples with SP layer demonstrate a more pronounced decrease in strain rate sensitivity with the increase of strain than samples with completely SP structure. Deformation in the SP layer proceeds as grain shear in a layer-by-layer manner. The deformation of SP layer through the operation of cooperative grain boundary sliding, i.e., sliding of grain groups as an entity along certain grain boundary surfaces, provides the main contribution to the total strain.
I. INTRODUCTION An equiaxed fine grained microstructure is an important prerequisite for superplastic performance which usually occurs at a strain rate of 10~4—10 3 s"1 and temperatures of 0.5-0.8 Tm (Tm being the melting point in degrees Kelvin).1'2 However, the microstructure of real commercial alloys is often nonuniform. The regions of fine grained microstructure (SP structure) may coexist with the regions of coarse grained or other types of non-SP structure that usually results in the degradation of the superplastic properties.1 Various types of geometrical arrangement and configuration of regions with SP- and non-SP structure may cause different deformation behavior of the entire deformed material. As has been reported for magnesium samples with regions of SP and non-SP structure connected either in parallel or in series with respect to the deformation axis,3 the parameters of mechanical behavior, i.e., flow stress and strain rate sensitivity, depend strongly on the volume fraction of regions with SP and non-SP microstructure and their configuration.
a)On
leave from Ufa State Technical University, Ufa 450025, Russia.
864
http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 4, Apr 1995
Downloaded: 16 Mar 2015
An arrangement of SP- and non-SP regions can be much more complicated in the technological process. For example, the situation where SP region is layered between non-SP regions at a certain angle with the loading direction may occur in welded titanium sheets subjected to the gas-forming process. An understanding of the deformation behavior of materials with such microstructures may give us better guidelines for control of their SP forming process. In addition,
Data Loading...
