Improvement Of Compressive Ductility Research Articles

Surface Martensite Strengthening of Ultra‐fine Porous Iron

The surface martensite strengthening of ultra‐fine isotropic porous iron has been performed via carburization and quenching treatment at 950 °C for 30 min. This paper is devoted to investigating the evolution of microstructure and related mechanical behavior of porous iron after carburization treatment. Results indicate that an effective carburization thickness (300 µm) contributes to a substantial improvement in compressive ductility (62%) and surface hardness (219 HV0.025) of carburized porous iron. Further, the quenching treatment after carburization produces the porous iron with an ultra‐fine martensite microstructure on surface layer that makes porous iron attain the highest yield strength (256 MPa) and energy absorption capacity (85 KJ kg−1). The major contribution of this present work is a demonstration that an improvement in mechanical properties of ultra‐fine porous iron can be achieved through the carburization and quenching treatment to control the phase structure on surface. Thus, the surface martensite strengthening is considered as a feasible method to prepare more valuable porous iron based alloys, and to provide them with more promising applications on key structural parts.

An atomic-scale insight into the effects of hydrogen microalloying on the glass-forming ability and ductility of Zr-based bulk metallic glasses

Notable improvements in both the glass-forming ability (GFA) and ambient temperature compressive ductility of Zr-based metallic glasses due to hydrogen microalloying have been reported by Granata et al. [1]. These two aspects of amorphous materials are considered to be mutually opposing properties in a metallic glass-forming system, usually explained via structural short-range order, local symmetry, structural free-volume and bonding character. To fundamentally understand why hydrogen simultaneously enhances GFA and ductility, ab initio molecular dynamic simulations were carried out on a Zr64Cu22Al12 alloy to assess how this element affects the local atomic configuration, electronic structure, chemical bonding and atomic transport processes. It is revealed that, while the addition of 1.5at.% H decreases the icosahedral order of the supercooled liquid over the entire temperature range studied, it decreases the diffusivity of the metallic constituents over the temperature range where heterogeneous nucleation is expected to occur. In this tradeoff between local structural stability and depressed crystal nucleation dynamics, the latter dominates in the H-containing alloy and the capacity for glass formation is enhanced. In addition, H was found to increase iconicity of the base glassy alloy, promote heterogeneity in the local structure and increase metallicity. In the competition between these opposing tendencies of chemical bonding and local structure to determine mechanical properties, the latter prevails and explains the experimentally-observed improvement in compressive ductility.

Microstructure, cold workability and strain hardening behavior of trimodaled AA 6061–TiO2 nanocomposite prepared by mechanical alloying

In the present work, the improvement of compressive ductility while maintaining high strength and toughness for nanocrystalline materials by cold upsetting (incremental loads) of bulk trimodaled composite was studied. Mechanically alloyed nanocrystalline (NC) AA 6061 alloy powders reinforced with nano TiO2 were blended with 0, 5, 10, 15, 20, 25, and 30 wt.% coarse grain (CG) elemental powders related to AA 6061 alloy composition to produce trimodal microstructure. The synthesized composite preforms were characterized by optical microscope, scanning electron microscope, transmission electron microscope and X-ray diffraction. The room temperature compressive deformation behavior was evaluated under triaxial stress state condition. With increasing percentage of CG phase in the nanocomposite, the gradual improvement in compressive ductility was observed at the cost of a small amount of strength but it favored the ease of deformation. The 15% CG trimodal composite exhibited an extremely high compressive strength of 935 MPa due to non-coalescence of individual CG particles and effective load transfer occurred in multi scale microstructures. But the 30% CG trimodal composite showed an incremental compressive ductility of around 16% while sacrificing a small amount of strength (845 MPa) and this composite displayed improved toughness (area under true effective stress and true effective strain curve) of over 600% than nanocomposite (0% CG). Also, the percentage cold workability of 30% CG composite was six times higher than that of 0% CG composite. Hence, the 30% CG trimodal composite was observed to be the good one as it exhibited a better strain hardening behavior while maintaining considerable strength and toughness.

Porous and Foamed Amorphous Metals

AbstractThis article reviews the state of the art in the field of porous amorphous metals by describing current processing techniques, mechanical properties, and potential applications. In addition to the reduction in density, the main benefit of introducing porosity in amorphous metals is the improvement in compressive ductility and energy absorption. This ductilizing effect is explained by: (1) shear-band interruption by individual pores at low porosities and (2) stable plastic bending of thin struts at higher porosities, with cellular amorphous metals displaying compressive ductilities of up to 80%.

Effect of copper alloying on the deformation behavior of B2 NiAl intermetallic compounds

The effects of copper addition on the compressive deformation behavior of B2 NiAl intermetallic alloys were investigated. Experimental NiAlCu alloys were vacuum melted and hot extruded at 1273 K at a 18:1 reduction ratio. Compressive flow behavior was analyzed over a temperature range from 298 to 1073 K. An increase in room temperature hardness by addition at 10 at% Cu was observed in near stoichiometric NiAl-z.sbnd;Cu alloys but hardnesses were lower in nickel-rich NiAlCu alloys than in binary NiAl. No considerable improvement in room temperature ductility was observed in NiAl containing 10 at% Cu. Significant improvement in compressive ductility was observed in copper-micro-alloyed (less than 1%) near stoichiometric NiAl. Fracture strains were in the range 1.25–0.35 at room temperature and reached 0.8 at 473 K. At over 673 K, copper-microalloyed NiAl deformed in an almost perfectly plastic manner. The sources of improved ductility are discussed.