Showing papers on "Superplasticity published in 1968"

Microstructure of superplastic alloys

Abstract: Studies are described which involve the routes to the equiaxed fine structure needed for superplastic behaviour in two-phase Zn–Al alloys. These indicate that the development of a spinodal structure is not an essential step towards achieving a superplastic structure in this alloy. Some microstructural aspects and mechanical behaviour characteristics of superplastic Zn–Al alloys are presented which suggest that the major mechanism of deformation in these alloys is crystallographic slip accompanied by grain boundary migration or recrystallization.

Microstructure of superplastic alloys

Abstract: The mode of decomposition of a eutectoid Zn–Al alloy has been related to the superplastic properties of the alloy. Decomposition during slow quenches or at high transformation temperatures produces a typical lamellar eutectoid structure with conventional mechanical properties. Decomposition at room temperature after a rapid quench produces a fine (∼ 1 μ) mixture of equiaxed zinc-rich and aluminium-rich grains and the alloy then shows tensile elongations of > 1000% at a deformation temperature of 250°C. It is proposed that the equiaxed structure is produced by spinodal decomposition.

Superplasticity in tungsten-rhenium alloys

Abstract: Superplasticity in W-Re alloys, noting tensile properties, grain size and strain rate sensitivity for various Re contents at high temperatures

The Role of Surfaces in Superplasticity

Abstract: The rate of neck growth in superplastic materials depends directly on surface irregularities and inversely on the strain rate sensitivity, m = (d lnσ/d lne). High values of m reflect a substantial contribution of diffusional creep, which is inversely related to a power function of the grain size. The characteristic maxima in the m versus log e curves is explained by the extension of the diffusional creep model to include a back stress, σo, which increases with impurity and inclusion content, and is greater in the rolling than in the transverse direction.

Solid metal molding

Abstract: THE SUPERPLASTIC EUTECTOID ALLOY OF ZINC AND ALUMINUM IS DEFORMED IN A DIE HAVING A TEMPERATURE SUBSTANTIALLY IN EXCESS OF THE CRITICAL TEMPERATURE LIMIT FOR THE ALLOY WITHOUT DETERMENTAL EFFECT. AFTER FORMING, THE TEMPERATURE OF THE RESULTING PART EXCEEDS THE CRITICAL LIMIT AND TO THUS ENABLE THE PART TO BE HANDLED WITHOUT DISTORTION. IN ADDITION, THE PART TEMPERATURE AFTER FORMING IS SUFFICIENTLY HIGH TO PERMIT IMMEDIATE HEAT TREATMENT FOR ROOM TEMPERATURE STRUCTURAL PROPERTY ENHANCEMENT AS PART OF THE FORMING CYCLE SIMPLY BY CONTROLLING THE COOLING RATE OF THE PART.

Improvements in or relating to a method of manufacturing pistons and to pistons produced by the method

Abstract: 1,254,884. Making pistons; extruding; working at specified temperatures. ASSOCIATED ENG. Ltd. 26 March, 1970 [30 Dec., 1968], No. 61776/68. Headings B3A, B3P and B3V. [Also in Division F2] A piston is made by backward extruding an alloy slug 20 which has been heated to a temperature range in which it is superplastic. The alloy may be aluminium-silicon with small amounts of alloying substances such as copper and magnesium. The temperature range for this alloy to render it superplastic is 200-300‹ C. and the slug may be heated before insertion into the die 21 or the die may be heated. The slug is cut from a length of continuous casting. After shaping the piston is machined to form gudgeon pin bores and ring seats.