Analysis of the Cold Compaction Behavior of Titanium Powders: A Comprehensive Inter-model Comparison Study of Compaction Equations
09 Jul 2015-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer US)-Vol. 46, Iss: 9, pp 4286-4297
TL;DR: In this article, the behavior and mechanisms of densification in selected titanium powders are critically analyzed by means of a comprehensive inter-model comparison of existing compaction equations, and results are discussed in terms of the comparative evaluation of cold uniaxial compaction tests of sponge Ti, CP TiH2, CP Grade 2 Ti, and TiH 2-SS316L nanocomposite powder samples, which were conducted at applied compaction pressures of up to 1250 MPa.
Abstract: A brief background to compaction equations and their application to titanium powder is presented. The behavior and mechanisms of densification in selected titanium powders is critically analyzed by means of a comprehensive inter-model comparison of existing compaction equations. The results are discussed in terms of the comparative evaluation of cold uniaxial compaction tests of sponge Ti, CP TiH2, CP Grade 2 Ti, and TiH2-SS316L nanocomposite powder samples, which were conducted at applied compaction pressures of up to 1250 MPa.
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Cites background from "Analysis of the Cold Compaction Beh..."
...Die pressing and sintering is the mostly used technology among all powder metallurgy processes [2,3]....
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TL;DR: In this paper, the influence of Nb content on microstructural evolution and tensile properties of Ti-Nb alloys was analyzed using optical microscopy (OM) and scanning electron microscopy equipped with energy dispersive spectrometer (EDX).
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TL;DR: A model based on the characterization of a single deformable particle under compression together with a power-law relation between connectivity and packing fraction results in outstanding predictions from the jamming point up to very high densities and allows a direct prediction of ϕ_{max} as a function of both the mixture ratio and the friction coefficient.
Abstract: We analyze the isotropic compaction of mixtures composed of rigid and deformable incompressible particles by the nonsmooth contact dynamics approach. The deformable bodies are simulated using a hyperelastic neo-Hookean constitutive law by means of classical finite elements. We characterize the evolution of the packing fraction, the elastic modulus, and the connectivity as a function of the applied stresses when varying the interparticle coefficient of friction. We show first that the packing fraction increases and tends asymptotically to a maximum value φ max , which depends on both the mixture ratio and the interparticle friction. The bulk modulus is also shown to increase with the packing fraction and to diverge as it approaches φ max. From the micromechanical expression of the granular stress tensor, we develop a model to describe the compaction behavior as a function of the applied pressure, the Young modulus of the deformable particles, and the mixture ratio. A bulk equation is also derived from the compaction equation. This model lays on the characterization of a single deformable particle under compression together with a power-law relation between connectivity and packing fraction. This compaction model, set by well-defined physical quantities, results in outstanding predictions from the jamming point up to very high densities and allows us to give a direct prediction of φ max as a function of both the mixture ratio and the friction coefficient.
19 citations
TL;DR: In this paper, a simple powder metallurgy process by sintering TiH2 powders was used to manufacture porous Ti components, and the effects of the processing parameters (pressure of cold isostatic pressing and sinting temperature) and the TiH 2/Ti ratio in the powder mixtures on the impurities, the linear shrinkage and the pore properties including overall and open porosities were comprehensively determined.
Abstract: A new simple powder metallurgy process by sintering TiH2 powders was used to manufacture porous Ti components. The effects of the processing parameters (pressure of cold isostatic pressing and sintering temperature) and the TiH2/Ti ratio in the powder mixtures on the impurities, the linear shrinkage and the pore properties (including overall and open porosities) were comprehensively determined. The addition of TiH2 as a reactant has been found beneficial for the synthesis of porous Ti components. The formation mechanisms of pores were demonstrated based on the dehydrogenation process of TiH2 during sintering, resulting in highest reactivity due to the “in statu nascendi” generation of the metal. In addition, the hardness and corrosion resistance of all the sintered samples were evaluated, related to the overall and open porosities. As a result, an optimal composition of Ti-40 wt.% TiH2 was defined, as its maximum open porosity was about 23%.
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TL;DR: In this paper, the effects of die wall lubricants on the cold compaction of titanium hydride powder are studied with respect to the green density and strength, green compact ejection force, and the occurrence of green compact cracking.
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References
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TL;DR: On the bicentenary of the publication of Poisson's Traité de Mécanique, the continuing relevance of Poissons's ratio in the understanding of the mechanical characteristics of modern materials is reviewed.
Abstract: In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by ½ and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt.
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TL;DR: There are two approaches to the problem of powder compression: (a) an observation of the relationship between pressure and volume, and (b) the distribution of internal stress and density as mentioned in this paper.
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