EFFECT OF SEVERE PLASTIC DEFORMATION ON STRUCTURE AND PROPERTIES OF AUSTENITIC AISI 316 GRADE STEEL
The article presents results of investigation of structure and properties of austenitic steel grade AISI 316 after application of Equal Channel Angular Pressing (ECAP) at the temperature of approx. 290C. The ECAP method leads to significant improvement of strength of investigated material. Investigation of structure was made by combination of TEM and FEG SEM together with EBSD. Statistic evaluation of angular disorientation and of size of grains/sub-grains was also made with use of electron diffraction (EBSD) in combination with scanning electron microscope FEG SEM Philips. It was proven that the ECAP method enables obtaining of ultra fine-grained austenitic structure. It was established with use of the EBSD technique that after 8 passes through the ECAP die the sub-grains with misorientation angles smaller than 10 formed less than 20% of the final structure. Average size of austenitic grains with high-angle boundaries after 8 passes was approx. 0.1m.
MECHANICAL PROPERTIES AND MICROSTRUCTURE OF Al ALLOY PRODUCED BY SPD PROCESS.
Aluminium alloy were subjected to ECAP process for grain refinemed to submicrometer levels. Microstructures after ECAP and subsequent annealing treatments were observed by using transmission electron microscope. Hardness and tensile tests were conducted on ECAP process alloys to examine the strength and elongation at ambient temperature. The hardness and strengths of ECAP processes alloy are higher considerably than those of commercially available respective alloy. Meanwhile, elongation is greatly decreasing after the second cycle and showing no further decrease with increasing the number of cycles. In the range of 5 to 8 cycles in ECAP process aluminium alloy exhibited strain hardening behaviour.
Hydrostatic Extrusion as a Method of Grain Refinement in Metallic Materials
The paper describes hydrostatic extrusion (HE) as a method of grain refinement of metallic materials down to the nanometric scale. The main features of this method are: (a) large strain, (b) very high strain rates (even greater than 104 s-1), and (c) deformation homogeneity. HE offers also the opportunity of obtaining bulk materials in a variety of forms (rods and wires of complex cross-sections, small tubes). The study undertaken on 4 materials (aluminium, aluminium alloy, copper and titanium) has shown that significant grain refinement , down to nanometric scale in the case of titanium and aluminium alloy, occurred during HE processing. This grain refinement produces significantly improved mechanical properties. It has been found that HE offers good prospects for the production of nano-structured metals and alloys.