Microstructure evolution and wear resistance of nitrogen-strengthened γ-Fe based alloy fabricated by N2 pressure sintering

Abstract

In the work, high nitrogen γ-Fe based alloy was fabricated by N2 pressure sintering in which the diffused N content could be up to 0.521wt%. Microstructure and mechanical properties were systematically studied. The increased activity of N atom with the added N2 pressure accelerated the generation of MnSiN2, which had an orthorhombic structure of an orientation relation of (11¯1)γ-Fe//(121¯)MnSiN2 with γ-Fe. HRTEM map displayed the incoherent interface of duplex phase on account of a large difference of the crystal plane distance between (11¯1)γ-Fe (d11¯1 = 0.2082 nm) and (121¯)MnSiN2 (d121¯ = 0.2428 nm). Besides, due to the solute N atoms in γ-Fe, an ordered structure with a superlattice structure of selective electron diffraction spots was formed. The elevated nanohardness for austenite grains implied the solution strengthening mechanism of N. The EBSD diagrams showed that the grain sizes of austenite are 9.81, 7.27 and 6.22um respectively, indicating that the formation and precipitation of MnSiN2 hindered the grain growth and led to the finer grain structure with the increased pressure of 0.05Mpa, 0.5Mpa and 1Mpa. The combination of solution strengthening and fine crystal reinforcing was the main reinforcement mechanism which enhanced the hardness austenite grains and wear resistance.

Keywords

• High nitrogen
• N2 pressure sintering
• Mechanical properties
• Wear resistance