HTMat

An Al2O3/5 vol%·ZrO2/5 vol% Y3Al5O12 (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO2 and YAG grains dispersed in a sub-micronic alumina matrix.

Wear and failure of die casting dies involve a complex interaction between various mechanisms. A CrAlSiN coating system was deposited on the base material, modulating the chemical composition of the chromium or the aluminium-silicon content. A set of the coated specimens was directly analysed through optical and electronic microscopy, so as to assess the overall quality. Other was subjected to a cyclic immersion program in molten aluminium bath. Coating efficiency was determined through electron microscopy analysis. Thermal fatigue was investigated, quantified.

A basic and a modified AISI H11 steels were selected for the research. Impact toughness and microstructure in the quenched and tempered state were analysed. Cyclic immersions in molten aluminium with the aim of simulating the washout, typical of aluminium die casting tools, were applied. Optical and electronic microscopy analysis were used to evaluate damages provided by washout on the specimen surface. XRD measurements were applied to identify the corrosion and soldering products deposited on the steel surface.

In this article an investigation has been carried out on different austempering cycles conducted on samples of the most diffused hot-work tool steel: AISI H 11. The laboratory tests have been addressed to the examination of the structure and to the evaluation of its mechanical properties: the hardness, the impact strength and the thermal fatigue.