Exploration On5CrMnMo Matrix ZrO₂Ceramic Layer Prepared By Injection Molding

When liquid forging, high temperature liquid metal have heat effects on moldmaterial, resulting in reduced mold life, restricting the further development of liquidforging technology, based on this,the paper proposes a method that is to make aceramic material surface modification of metallic materials to improve theperformance of the mold material.Putting a thickness of the ceramic layer on thepunch surface by ceramic powder injection molding technique, the ceramic andmetal have a mechanical connection, so that the mold will have high hardness, wearresistance and high temperature performance characteristics, in order to promoteliquid forging technology development.Through the study of5CrMnMo matrix ZrO2ceramic layer prepared byinjection molding,and the use of density measurement, linear shrinkagemeasurement, DSC and TGA analysis, Vickers hardness tester, SEM, infraredthermometer, friction and wear tester, furnaces, etc. analytical tools and methods,itget some results.By the exploration of zirconia injection molding, the result showed that theinjection molding of ZrO2powder’s loading was50%-55%, the zirconia powder’sloading can be improved by surface modification, the powder loading wassuccessfully increased to55%, in favor of the subsequent sintering and reduced theshrinkage of zirconia.By trial and error of extrusion granulation process, found thatadding sequential feed ingredients, mixing temperature, mixing time, and thesqueezing number will have varying degrees effect on granulation effects,By trialand error of extrusion granulation process, found that adding sequential feedingredients, mixing temperature, mixing time, and the squeezing number will havevarying degrees effect on granulation effects.The optimum mixing process is:Firstthe original zirconia powder was heated to175℃in the smelting furnace, followedby addition of polypropylene,a little uniformly stirring for20min; then cooled to150℃, stearic acid was added, a little stirring, heat10min; adding paraffin mixed with half of the powder by stirring to obtain a low viscosity of the kneaded clay, andthe remaining powder was then gradually mixing until uniform;finally cooled to130℃thermal insulation sufficiently to mix evenly; then another five times toextrusion granulation. Thus prepared a good uniformity of the zirconiafeed.Through exploration of the injection molding process parameters, got theoptimum injection molding process parameters: the injection zone temperature is185℃, the melt zone temperature is190℃, the injection rate is75%of themaximum speed of the system, the injection time is6.5seconds, dwell time is10s,mold temperature is40℃; and analyze the mechanism of injection molding ofvarious defects.By inquiry of degreasing and sintering processes found that each component ofthe adhesive’s thermal decomposition temperature and interval are verydifferent,Wherein the paraffin’s severe decomposition temperature zone is220-320℃, polypropylene severe’s decomposition temperature region is320-380℃, and theamount of stearic acid when at about165℃it has begun to slowlydecompose.When the sintering temperature increases, the density of the zirconiumoxide ceramic layer and the linear shrinkage density increases, the grain becomeslarge, but the porosity will decrease; the higher sintering temperature, the moresmooth the surface of zirconia.After sintered at1200℃, zirconia’s density, density,porosity, and the linear shrinkage rate were5.49g/cm3,90.16%,9.84%,10.83%, andafter1300℃,zirconia’s density, density, porosity, and linear shrinkage were5.68g/cm3,93.11%,6.89%,13.73%.Characterized by the hardness of Vickers hardness of zirconia ceramics and themold base,it was found significantly that the zirconia is better than5CrMnMo;In theinsulation experiment, the insulating effect of zirconia is very good, at450℃and700℃,the insulation effect was about100℃, that can be a good tool to reduce thework temperature of the mold;In the friction and wear experiments, under differentpressure load,zirconia’s wear significantly is better than die steel, it’s frictioncoefficient is relatively small, and the wear microstructure surface is more smooththan tool steel; In the heat cycle test, the number of thermal shock of the zirconiaceramic layer was45on average, indicating that the coating has a good combination of strength and thermal shock resistance,Because of much more demanding than theactual operating conditions during the design of the experiment, so the actualthermal shock resistance in liquid forging will be better, and mold life will also hasa corresponding guarantee.