Powder Metallurgy Tool Research Articles

Using the P-δ2 analysis to deconvolute the nanoindentation response of hard-coated systems

The continuously recording indentation responses of a number of coated systems, mainly thin (<10 μm) hard nitride coatings on stainless steels and a powder metallurgy tool steel, have been explored using nanoindentation with indenter displacements increasing progressively to values greater than the coating thickness. The resultant load-displacement data have been analyzed not only to produce conventional load-displacement (P-δ) plots but also to examine the relationship between P and δ2. Recent models have proposed that there should be a linear P-δ2 relationship for homogeneous systems and that such plots have the potential to reveal the load/displacement regimes in which either the coating or the substrate, or both, are dominant in controlling the overall behavior of the coated system. By utilizing point-to-point differentiation of the P-δ2 relationship, this paper extends this approach to confirm not only that these different regimes of behavior may be readily experimentally identified in this way, but also that further details, such as the propagation of cracks, may be recognized. Our analysis also provides a valuable experimental link to models describing the near-surface deformation behavior of coated systems.

The effects of surface corrosion on the fatigue behaviour of aluminium alloy specimens containing cold expanded holes : Glinos, N., Wagstaff, P.G. and Cook, R. Computational Methods Testing for Eng. Integrity (1996) 61–70 Conference: First International Conference on Computational Methods and Testing for Engineering Integrity, Kuala Lumpur, Malaysia (19–21 Mar. 1996)

The paper details experimental research on the surface modification/alloying and combined electrical discharge texturing (EDT) of hardened AISI D2 Sendzimir rolls, used for the production of stainless steel strip. Test results are presented when using powder metallurgy (PM) green compact and sintered electrodes—TiC/WC/Co and WC/Co, as a means to improve roll life and performance. Two- and three-dimensional surface roughness assessments showed the topographical characteristics of EDT samples processed using PM electrodes, to be similar to those found when using conventional copper or graphite tools, with the same pulse generator parameters. GDOES analysis showed that Ti and/or W contained in the PM electrodes, together with C decomposed from the dielectric medium during sparking, were transferred to the workpiece surface. Microhardness measurement of roll cross-sections indicated an increase in white layer hardness of ∼300 HK (0.025) when employing sintered TiC/WC/Co tools, compared with conventionally processed EDT rolls. In rolling trials using mill rolls textured with PM tool electrodes, roll/strip texture transfer measures (Ra and Pc), were consistently higher for the TiC/WC/Co textured rolls, indicating less roll wear.

Ultrahigh vanadium wear resistant cold work tool steels : W.B.Eisen et al. (Crucible Research, USA.)

Powder metallurgy tool steels are technologically well established, being employed in several applications. However, for certain situations, as in the case of components submitted to severe wear, it is necessary to enhance its surface properties. Among the surface hardening techniques, ion nitriding has proven to be a good candidate for treating powder metallurgy tool steels, since the parts are less susceptible to distortions, as can occur on other conventional surface treatments. The objective of this work was the verification of the effect of vanadium on ion nitriding and, consequently, on wear behavior. The alloys with different vanadium contents were ion nitrided at 550 °C for 1, 3, and 5 h. The nitrided layers were characterized by microhardness test, optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and pin-on-disk test. The hardness values of the layers enhanced significantly after ion nitriding treatment, due to the formation of VN. The wear test revealed that hardness enhancement resulted in a lesser mass loss for a compound layer of VN and γ′-Fe4N. The treatment time did not influence the shape and size of carbides present in these steels.

Sinterability of powder metallurgy tool steels produced with the application of heat-time treatment of the melt

Powder metallurgy tool steels prepared from the powders of gas-atomized melts subjected to heat-time treatment were studied. Material containing above 1.2% carbon, in addition to tungsten and molybdenum, exhibited a porosity decrease of 6–12% after vacuum sintering at a temperature 70°C lower than that of solid-phase sintering. The increased sinterability of the alloys was related to the presence of a high, close to eutectic, carbon concentration at the surface of fine powder particles (principally 50–100 μm), and its explained by the formation of liquid phase during the process of leveling the element concentration gradients.