There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Materials for additive manufacturing

Refining a metal’s grain size can result in dramatic increases in strength, and the magnitude of this strengthening increment can be estimated using the Hall–Petch equation. Since the Hall–Petch equation was proposed, there have been many experimental studies supporting its applicability to pure metals, intermetallics and multi-phase alloys. In this article, we gather the grain-size strengthening data from the Hall–Petch studies on pure metals and use this aggregated data to calculate best estimates of these metals’ Hall–Petch parameters. We also use this aggregated data to re-evaluate the various models developed to physically support the Hall–Petch scaling.

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Six decades of the Hall–Petch effect – a survey of grain-size strengthening studies on pure metals

Hall-Petch relationship in Mg alloys: A review

Effective values of critical resolved shear stress for slip in polycrystalline magnesium and other hcp metals

Sensitivity of deformation twinning to grain size in titanium and magnesium

Yield point elongation due to twinning in a magnesium alloy

In this paper, we printed Ti-6Al-4V SLM parts based on Taguchi design of experiment and related standards to measure and compare hardness with different mechanical properties that were obtained in our previous research such as density, strength, elongation, and average surface. Then the effect of process parameters comprising laser power, scan speed, hatch space, laser pattern angle coupling, along with heat treatment as a post-process, in relation to hardness was analysed. The relation of measured factors with each other was also studied and related mechanisms were discussed in depth. The original contribution in this paper is in producing a large and precise dataset and the comparison with mechanical properties. Another contribution is related to the analysis of process parameters in relation to hardness and explaining them by rheological phenomena. The results showed an interesting similarity between hardness and density which is highly related to the formation of the melting pool and porosities within the process.

Alireza Ghaderi

Papers

Sensitivity of deformation twinning to grain size in titanium and magnesium

Yield point elongation due to twinning in a magnesium alloy

The effect of SLM process parameters on density, hardness, tensile strength and surface quality of Ti-6Al-4V

Effect of graphite morphologies on the tribological behavior of austempered cast iron

Influence of orientation on twin nucleation and growth at low strains in a magnesium alloy