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This paper presents experimental results relating the initial austenite grain size to bulk hardness, compressive yield stress (σ 0.2% ) and volume fraction of stress-induced ε martensite. It is shown that the bulk hardness obeys quite closely the Hall-Petch equation while the yield stress, σ 0.2% , decreases with decrease of grain size, indicating that the induction of ε martensite mechanically is easier for the materials with finer grains. This fact is corroborated by the observed increase of the volume fraction of stress-induced ε martensite with decrease of grain size. Inversely, after shape recovery heating, the volume fraction of residual stress-induced ε martensite increases as the grain size increases, e.g. the increase in grain size hinders the reversible martensitic transformation.

cannot be applied. The mechanical response for external loads is then better simulated by instrumented indentation performed on ion beam modified surfaces rather than on cross-sections.In the present work we report a comparative study about structural, mechanical and tribological properties of AISI 304 and AISI 316 stainless steels submitted to nitrogen glow discharge at different substrate temperatures from 300 to 500 °C. Structural characterization was evaluated by X ray diffraction (Bragg-Brentano geometry) using Rietveld refinement. Hardness, elastic modulus profiles and surface topography were obtained by instrumented indentation. Conventional Vickers measurements were also employed in order to obtain deeper hardness profiles. Tribological and wear behavior were studied by reciprocating sliding tests. Experimental ProcedureCommercial sheets of AISI 304 (Ni 8.63%, Cr 16.04%, C 0.047%, Si 0.48%, Mn 1.37%, S 0.005%, Mo 0.09%, P 0.029% weight, with Fe being the balance) and commercial rods of AISI 316 (Ni 11.64%, Cr 15.68%, C 0.10%, Si 0.34%, Mn 1.73%, S 0.031%, Mo 1.86%, P 0.029% weight with Fe being the balance) were cut in 1.5 x 1.5 x 0.5 cm and φ = 3 cm and 0.5 cm thick pieces, respectively. The samples were mechanically polished up to ¼ µm diamond paste in order to obtain a final mirror finish.DC glow discharge was performed in N 2 :H 2 -20:80 atmosphere at 600 Pa with prior H 2 sputtering at 100 °C during 2 hours. The plasma current ranged from 200 to 300 mA, resulting in sample ensembles with substrate temperatures of 300, 400 and 500 °C. The temperature was controlled by monitoring a backside thermocouple and adjusting the plasma current as needed. All samples were nitrided during four hours. Mechanical and tribological properties of AISI 304 and AISI 316 stainless steels submitted to glow discharge ion nitriding are reported. The atmosphere was 20:80 -N 2 :H 2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γ N ) in both steels. Increasing the temperature, the phases γ′-Fe 4 N and ε-Fe 2+x N were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.

The temperature induced phase transition in MnAs is analyzed in this work using X ray Rietveld refinement. The results show the presence of the hexagonal phase (P6(3)/mmc) at room temperature and the first-order structural-magnetic transition to the orthorhombic phase (Pnma) around 318 K was followed in detail. The MnAs magnetic characterization allowed to obtain the transition temperature and a maximum value of 47 J/(kg.K) for the measured magnetocaloric effect for a magnetic field variation of 5 T

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