Case Study What die materials and fabricated structures could be investigated to allow for semi- solid steel forming?

Ceramic die materials Characteristics required Mechanical – Strength, Wear, Fatigue Thermal shock Thermal fatigue Corrosion Oxidation 1. She, J., and Ohji, T., Thermal shock behavior of porous silicon carbide ceramics, J. Am. Ceram. Soc., 85, 8, Meyer-Rau, S. and Telle, R., Testing strategies for corrosive interaction of ceramics with semi-solid and molten metal alloys, J. of European Ceramic Society, 25, Evans, H., and Taylor, M., Oxidation of high temperature coatings, J. Aerospace Engineering, IMechE, 220, Part G, Velay, V., et al., A continuum damage model applied to high temperature fatigue lifetime prediction of a martensitic tool steel, Fatigue Fract Engng Struct, 28, 2005.

Ceramic die materials Partially stabilised zirconia – US (81) and by Mg, Ca or Y additions CA (79) Cermet casting mould – FR (Renault) –alumina in Fe, Cr, Al mix; pressed between 7000 and 70,000 psi and sintered between 2190 and 2640 deg F; TBC / lubricants applied: alumina, silica, silico-aluminate, graphite, lamp or acetylene black

Metal die materials H13 tool steel –reduce heat checking by substituting with material with higher elevated mechanical properties –reduce magnitude of thermal stress, for example, by increasing the bulk metal die temperature Ni based super alloys –e.g. INCONEL, Cr-Ni-Mo Electroslag cast steel –good ductility and toughness as well as high tensile strength at elevated temperatures - important for high thermal shock resistance 1.Sakhuja, A., and Brevick, J., Prediction of thermal fatigue life in tooling for die-casting copper via finite element analysis, Am. Inst. Phys., Fang, J., et al., The characteristics of fatigue under isothermal and thermo-mechanical load in Cr-Ni-Mo cast hot die steel, Fatigue Fract Engng Struct, 25, Moon, Y., Kim, J., and Tyne, C., Thermal shock resistance of electroslag cast steel for hot working tools, J. Mat. Proc. Tech., , 2004.

Die fabtrication methods Machining from bulk feedstock – conventional Sintering – metal and ceramic feedstock Cladding by shrink fitting – GKN Patent US (73) Multiple layer ceramic – similar to LOM principle – EP (2000) –glass & alumina powder sintered into 0.2 mm thick sheets; applicable to metal carbides: B 4 C, SiC, & TiC and metal nitrates: Si 3 N 4, BN, & TiN Sialon ceramic with metal coating – JP (89) – and sialon with metal compound coating film e.g. super hardened Ti, Si, … film, by ion planting Clamped ceramic columns of polygon cross section – JP (88) –applicable with metal oxide or metal nitride (e.g. Si 3 N 4 and ZrO 2 ) Mould insert used as cladding – WO (06) –from developer of melt away core process

Fabricated die structure Bulk metal Bulk ceramic Cermet Layered structure / Hybrid structure Channels for heating/cooling cartridges / heat transfer fluid Inserts / shapes that reduce heat build up