Effect of Ni-P content on microstructure and mechanical properties of Fe-Ni-P alloy

A series of Fe-Ni-P alloys with different Ni-P contents were prepared by micro-press sintering,and the influence of the contents on the final microstructure and mechanical properties was evaluated.Sample Fe-34(Ni,P)contains the highest Ni-P content(34.18 wt.%)and its relative density reaches 98.75%,which is attributed to the introduction of an appropriate amount of liquid phase during the sintering process.The main phase of the sample is transformed from a to c phase under the gradual increment of Ni-P content.Simultaneously,a large number of phosphides that have strong inhibition on the migration and expansion of grain boundaries are precipitated on the matrix,and synergistic effect with low-temperature sintering results in partial grain refinement.The samples with high Ni-P content have a high volume of c phase,which makes the sample show the optimal plasticity under the maximum compressive load.And the fracture mode has also changed from brittle fracture to a mixed mode of brittle and ductile fracture.The decrease in the proportion of a phase has a weakening effect on the strength,but the refinement of the grain and the increase in the phosphide are the factors that increase the strength,so that the degree of manifestation varies in different Ni-P levels.

Preparation and compression behavior of Fe-Ni-P/porous-Fe/Fe-Ni-P composites

Porous-Fe-N alloys designed for light weight or energy absorption are inevitably facing the compromise of deteriorated mechanical properties. To optimize their mechanical properties, here a novel Fe-Ni-P/porous-Fe/Fe-Ni-P composite with sandwich structure was fabricated by spark plasma sintering and further strengthened via cryogenic treatment. Based on the principle of solid phase sintering and transient liquid phase sintering, porous core and dense outer layers formed simultaneously after co-sintering. The as-fabricated samples show excellent compressive strength of 1708 MPa, and after cryogenic treatment, due to the sufficient martensitic transformation, Fe-Ni-P outer layers show substantially increased hardness from 246.7 to 386.6 HV_(0.1)while the porous-Fe core remains unchanged. And the compressive strength maintains 1424 MPa despise the aggravated incongruity of deformation. The ratio of constituent microhardness R has been proposed to represent the hardness matching, and with decreasing R, the incongruity of deformation is intensified, and the nominal compressive strength is reduced.

Crystallographic Texture Evolution of ■-Fe_4N and Its Influences on Tribological Property of Nitrided Steel

The crystallographic texture of γ′-Fe4N in compound layer and its influences on the tribological properties of nitrided steel 38CrMoA1 are investigated in the study.The preferred orientation of（200）γ′is produced by low-temperature nitriding in atmosphere with low nitrogen-hydrogen ratio and increases with the nitriding time.The preferred orientation of（220）γ′appears after 72 h cyclic nitriding.The orientation relationships（0001）ε,/（101）α′,and[ll0]J/[111]γ′（Ill）γ′/（0001）α′ and[011]γ′//[1210]ε,（200）γ′//（l10）α′,and[011]γ′//[111]α′,as well as（1T03）J（220）γ′,and[0100]J/[110]γ′,are established by first-principles method.The misfit of interatornic distance（δ）,determining the phase transition resistance,is calculated.Accordingly,two reaction pathways during nitriding,and α′→γ′and α′→ε→γ′,are assumed,which determines the preferred orientations of γ′-Fe4N.Results of wear tests demonstrate that the specimen with preferred orientation of（200）γ′ exhibits lower frictional coefficient and lower wear rate in comparison with the specimen with（220）γ′ preferred orien-tation.（111）γ′ texture usually relates to the lower frictional coefficient but higher wear rate due to the main slip system parallel to the sliding plane.Therefore,the（200）γ′ preferred orientation has a positive significance in improving the wear properties of steels.