Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microsc...Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microscopy and scanning and transmission electron microscopy (TEM). Chemical compositions for the oxide scale and near surface zone were also analysed. The results obtained show that the oxide scale developed in vacuum exhibits a distinct structure from that developed in air. Comparing to the vacuum-developed scale, the air-developed scale possesses a more complicated structure and relatively poor adhesion to the matrix. TEM observations reveal a difference in the dislocation density in the vicinity of the free surface, near-surface zone and the core of the specimens examined.展开更多
The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized ...The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized as coatings materials. Tensile tests were carried out in the temperature range of Portevin-Le Chatelier (PLC) effect It has been found that grains at edges and corners of the 316 steel specimens have been dramatically constricted by grit blasting and spraying. Grit blasting has been found to exert a shot-peening effect on the mechanical properties of 316 steel specimens. Coatings with lower values of coating volume fraction strengthen the coated specimens in the very similar way as blasting. While if the volume fraction of coating, (Vv)c, exceeds a critical value, (VV)K, softens the specimens. Specimens with low values of (Vv)c, have high values of flow stress, as well as higher values of work-hardening coefficient, Calculations based on the experimental results show that the high thickness coatings have relatively lower contribution to the mechanical properties of specimens.展开更多
Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying...Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying loads in the range of 25-1000μN. Simultaneously, AFM images of the sample surface were recorded before and after indentation process .For type 316 stainless steel, the indentation size effect was found. The results were discussed in the terms of the model of geometrically necessary dislocations proposed to interpret the indentation size effect.It can be seen that the square of the nanohardness, H 2, vs the inverse of indentation depth, 1/h, is linearly dependent on the indented depth in the range of 25-150nm,which is a good qualitative agreement with the predictions of the model. However, for shallow indents, the slope of the line severely changes.Some possible mechanisms for this change were proposed.展开更多
Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into acc...Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.展开更多
文摘Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microscopy and scanning and transmission electron microscopy (TEM). Chemical compositions for the oxide scale and near surface zone were also analysed. The results obtained show that the oxide scale developed in vacuum exhibits a distinct structure from that developed in air. Comparing to the vacuum-developed scale, the air-developed scale possesses a more complicated structure and relatively poor adhesion to the matrix. TEM observations reveal a difference in the dislocation density in the vicinity of the free surface, near-surface zone and the core of the specimens examined.
文摘The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized as coatings materials. Tensile tests were carried out in the temperature range of Portevin-Le Chatelier (PLC) effect It has been found that grains at edges and corners of the 316 steel specimens have been dramatically constricted by grit blasting and spraying. Grit blasting has been found to exert a shot-peening effect on the mechanical properties of 316 steel specimens. Coatings with lower values of coating volume fraction strengthen the coated specimens in the very similar way as blasting. While if the volume fraction of coating, (Vv)c, exceeds a critical value, (VV)K, softens the specimens. Specimens with low values of (Vv)c, have high values of flow stress, as well as higher values of work-hardening coefficient, Calculations based on the experimental results show that the high thickness coatings have relatively lower contribution to the mechanical properties of specimens.
基金FundedbytheNationalNaturalScienceFoundationofChi na (No .5 0 1710 13)andtheSpecialFoundationfortheNationalStateBasicResearchProject(No.G19990 6 5 0 )
文摘Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying loads in the range of 25-1000μN. Simultaneously, AFM images of the sample surface were recorded before and after indentation process .For type 316 stainless steel, the indentation size effect was found. The results were discussed in the terms of the model of geometrically necessary dislocations proposed to interpret the indentation size effect.It can be seen that the square of the nanohardness, H 2, vs the inverse of indentation depth, 1/h, is linearly dependent on the indented depth in the range of 25-150nm,which is a good qualitative agreement with the predictions of the model. However, for shallow indents, the slope of the line severely changes.Some possible mechanisms for this change were proposed.
文摘Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.
