Surface Nanocrystallization by Surface Mechanical Attrition Treatment

Abstract

Based on strain-induced grain refinement, a novel surface mechanical attrition treatment (SMAT) technique has been developed to synthesize a nanostructured surface layer on metallic materials in order to upgrade their overall properties and performance without changing their chemical compositions. In recent several years, the microstructures and properties of surface layer were systematically investigated in various SMAT metals and alloys, including b.c.c., f.c.c. and h.c.p. crystal structures. Different grain refinement approaches and nanocrystalline formation mechanisms were identified in these deformed materials, involving dislocation activities, mechanical twinning and interaction of dislocations with mechanical twins. The properties of the surface layer were measured by means of hardness, tensile, fatigue and wear tests. The enhanced properties of the surface layer are mainly attributed to the strain-induced grain refinement. In this work, we reviewed the microstructures and properties of surface layer in the SMAT materials.

Formation of Surface Nano/Ultrafine Structure using Deep Rolling Process on the AISI 316L Stainless Steel

“…19 In general, intersecting mechanical twins with lower sizes are formed near to surface regions contained highest value of induced strain and then transformed to the nano/ultrafine grains. 20 While, lamellar and intersecting mechanical twins with further sizes and without any refined grain are formed in high depths contained lower strain. 20 For example, selected lamellar twins (LT) in Figure 3 have about 1200 nm thickness and refined grains are not shown in this part.…”

“…20 While, lamellar and intersecting mechanical twins with further sizes and without any refined grain are formed in high depths contained lower strain. 20 For example, selected lamellar twins (LT) in Figure 3 have about 1200 nm thickness and refined grains are not shown in this part. While at low depths of Figure 4, thickness of lamellar twin (LT) is near to 400nm and refined grains are shown in this part.…”

“…The martensitic transformation can be attributed to the formation of intersecting twins in the surface layers, due to the relatively low stacking-fault energy of austenitic stainless steels. [19][20][21][22][23] The feritscopy measurements showed that 8 and 11Vol.% of ' α martensite have been formed in the deformed zones of the DRI and DRII processed kinds, respectively. Comparison of X-ray patterns and feritscopy measurements reveals that a further amount of martensite (about 11 Vol.%) has been produced in the DRII sample with higher intensity of martensite peaks.…”

“…[13][14][15][16][17][18][19][20] In austenitic stainless steels, formation of martensite phase is achieved at locale of twins intersecting. On the other hand, intersection of two sets of mechanical twins leads to transformation of austenitic phase to martensitic kind.…”

“…On the other hand, intersection of two sets of mechanical twins leads to transformation of austenitic phase to martensitic kind. [13][14][15][16][17][18][19][20] Due to observation and recognizing of martensitic phase by SEM needs to the BSE detector, LT and IT cannot be strain-induced martensite. Refined grains and mechanical twins have not been formed in the substrate (S), due to the low strain induction by the performed deep rolling.…”