General relationship between strength and hardness

► The hardness is not an intrinsic property but reflects the hardening state in CG. ► The ratio of hardness to strength can also be reflected by indentation morphology. ► The ratio of hardness to strength increases with increasing parameter α. ► H V = 3 σ UTS is valid for materials with relatively h...

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Published in:	Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-11, Vol.529, p.62-73
Main Authors:	Zhang, P., Li, S.X., Zhang, Z.F.
Format:	Article
Language:	eng
Subjects:	Brittleness Bulk metallic glasses Ceramics Condensed matter: structure, mechanical and thermal properties Crystalline materials Deformation and plasticity (including yield, ductility, and superplasticity) Exact sciences and technology Hardness Indentation Mechanical and acoustical properties of condensed matter Mechanical properties of solids Microstructure Morphology Physics Strength Tribology and hardness Yield criterion Zirconium
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Summary:	► The hardness is not an intrinsic property but reflects the hardening state in CG. ► The ratio of hardness to strength can also be reflected by indentation morphology. ► The ratio of hardness to strength increases with increasing parameter α. ► H V = 3 σ UTS is valid for materials with relatively high strength and better toughness. Both hardness and strength are the important properties of materials, and they often obey the three times empirical relationship in work-hardened metals and some bulk metallic glasses (BMGs). But the relationships between strength and hardness are quite different for those coarse-grained (CG) and ultrafine-grained materials, brittle BMGs and ceramics. In the present work, some Cu alloys with different microstructures, Zr-, Co-based BMGs and Al 2O 3 were employed to analyze the general relationship between hardness and strength. Several different relationships could be gotten from the experimental results of different materials available, and three types of indentation morphologies were observed. Indentation with “sink-in” morphology always represents a state of material and one third of hardness is in the range from yield strength to ultimate tensile strength. The other two indentation morphologies induced the fully hardening of material, so hardness could represent the intrinsic mechanical property of materials. The ratios of hardness to strength are found to be affected by the piled-up behaviors and their ability of shear deformation. Combined effect of the two aspects makes hardness approximately be three times of strength in the work-hardened crystalline materials and the shearable BMGs, but higher than three times of strength in the brittle-, annealed BMGs and ceramics.
ISSN:	0921-5093 1873-4936