Miroslav Greger

Twist channel angular pressing (TCAP) as a method for increasing the efficiency of SPD

The paper proposes a new variation for the application of SPD methods. Suggested TCAP (twisted channel angular pressing) technology obtains the larger imposed strain more effectively while increasing homogeneity of material. The number of passes needed to obtain the ultra-fine to nano-scale grains in bulk materials can be significantly reduced. Commercially pure copper (99.97%) was used for the experimental verification of the suggested process. The thermal stability of extruded copper was studied after the application of two modes of heat treatment. The deformation parameters of the process were also described using the numerical simulation based on FEM analysis. Predicted value of imposed strain, after a single pass, reached approximately 2.3. Measured strength, determined after four passes, achieved values around 440 MPa homogeneously along the cross-section of the extruded material. The grain size, determined after four passes, averaged out 1.2 μm. Homogeneity of deformation was also confirmed by micro-hardness tests.

FEM simulation of extrusion by ECAP method on magnesium alloy AZ91

The simulation of extrusion process by (ECAP) technique, which involves a simple large shear deformation during passage through two intersecting channels, was applied to the AZ91 Mg alloy to obtain an ultrafine-grained microstructure. For the stress and strain intensity investigation, computer simulation was used. Temperature dependences of extrusion process have been detected along with others. Four pressings were conducted at 250?C, while the fifth pressing was conducted at 180?C. The grain refinement and homogeneity of grain-size distribution increased with pass number. Temperature of process was measured during pass and decreased with respect to the number of pass along with obtaining finer grains. Finite Element Method (FEM) simulation was examined on AZ 91 alloy by practical tests. The experimental result agreed well with that obtained from numerical analyses carried out based on the FEM. Presented paper shows evidences that this forming method is an efficient tool for improving the mechanical properties. [Received 15 March 2006; Accepted 9 March 2007]

Hot deformation behaviour and grain refinement of intermetallic compound Ni3Al

The paper describes the preparation of Ni3Al-based intermetallic compounds and investigations of their structures in the ascast, worked, and annealed states. The performed experimental works approved a possibility of hot working of the highly brittle polycrystalline intermetallic compound Ni3Al with large grain cast structure. The facility of originating the recrystallization seems to be surprising in such a material. On the other hand, the growth of recrystallization nuclei is strongly retarded. The case is further complicated by the fact of heterogeneous deformation in the microvolume. Microalloying with boron or zirconium influenced the original structure parameters as well as the optimum deformation temperature. Simultaneously the probability of a transgranular cleavage fracture increased. For the stoichiometric Ni3Al intermetallic compound the optimum deformation temperature 1150 °C has been assessed. At temperature 1250 °C, the alloy Ni3Al + 0,1 at. % B manifested the best plasticity. The special type of rotary working combined with friction heating gave the best results from point of view of obtaining a fully recrystallized region.

Effect of Severe Plastic Deformation on Structure and Properties of Beta Titanium Alloy Using for Hip Implants

The Paper Deals with Microstructural and Mechanical Properties Changes during Severe Plastic Deformation Process in Beta Titanium Alloy Used for Hip Implants. Effect of Various Numbers of Passes through ECAP (Equal Chanel Angular Pressing) Die on Microstructure and Properties Have been Evaluated. Comparison between Virgin State Cast Alloy and Alloy after Several Steps of Severe Plastic Deformation Induced by ECAP Technology Have been Carried out. Mechanical Properties Have been Evaluated Using Miniaturized Specimens. from Experimental Work can Be Concluded Positive Effect of ECAP Technology both on Mechanical Properties (yield Stress as well as Tensile Strength) Including Grain Size.