Study on Crystallographic Texture in Compound Layer Produced during Plasma Nitriding of Steels

摘要

The crystallographic texture of γ' in the compound layer and its influences on the tribological properties of nitrided steel 38CrMoA1 are investigated in this paper.The preferred orientation of (200)γ' is produced under the nitriding condition of low temperature and low nitrogen containing atmosphere and increases with the nitriding time.The preferred orientation of (220)γ' appears in the surface layer after 72 h cyclic nitriding.Such orientation relationships (ORs), (0001)ε//(101) α' and [110] ε//[111]α', (111) γ'//(0001)εand [011]γ'//[1 (2)10] ε, (200)γ'//(110)α' and [011]γ'//[111]α', as well as (1 (1)03)ε//(220)γ' and [0100]ε//[1 (1)0]γ' are established, based on which the misfit of interatomic distance (δ) is calculated.The value of δ is an indicator of phase transition resistance.Therefore, two kinds of reaction pathways during nitriding: α'→γ' and et'→ε→γ' can be assumed.In addition, the observed preferred orientations have close relationship with the reaction pathways.Results of mechanical tests show that the preferred orientation of (200)γ' usually results in lower frictional coefficient and wear rate in comparison with the preferred orientation of (220)y'.(111)γ' texture usually relates to the lower frictional coefficient but higher wear rate, due to the slip system parallel to the sliding plane.Therefore, the preferred orientation of (200)γ'has a positive significance in improving the wear properties of steels.