(Ca,Sr,Ba)ZrO_(3):A promising entropy-stabilized ceramic for titanium alloys smelting

A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550℃.The relative density and hardness of the ES(Ca,Sr,Ba)ZrO_(3) ceramic sintered at 1550℃are 97.79%and 10.840.33 GPa,re s pectively.This ES(Ca,Sr,Ba)ZrO_(3) exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates,CaZrO_(3),SrZrO_(3) and BaZrO_(3).Most importantly,the ES(Ca,Sr,Ba)ZrO_(3) ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES(Ca,Sr,Ba)ZrO_(3) ceramic in the contact region.The combination of these properties indicates that ES(Ca,Sr,Ba)ZrO_(3) ceramic is promising for use as a novel crucible material for the melting of titanium alloys.

Medium-entropy(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta):Promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking

With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature thermal radiation.Besides,poor corrosion resistance of YSZ to molten calcia-magnesia-alumina-silicates(CMAS)also impedes its application in sand,dust,or volcanic ash laden environments.In order to improve the hightemperature thermal radiation shielding performance and CMAS resistance of YSZ and further reduce its thermal conductivity,two medium-entropy(ME)oxide ceramics,ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),were designed and prepared by pressureless sintering of binary powder compacts in this work.ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)presents cubic structure but a trace amount of secondary phase,while ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)displays a combination of tetragonal phase(81.6 wt.%)and cubic phase(18.4 wt.%).Both ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)possess better high-temperature thermal radiation shielding performance than YSZ.Especially,the high-temperature thermal radiation shielding performance of ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)is superior to that of ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)due to its narrower band gap and correspondingly higher infrared absorbance(above 0.7)at the waveband of 1 to 5μm.The two ME oxides also display significantly lower thermal conductivity than YSZ and close thermal expansion coefficients(TECs)to YSZ and Ni-based superalloys.In addition,the two ME oxides possess excellent CMAS resistance.After attack by molten CMAS at 1250℃for 4 h,merely~2μm thick penetration layer has been formed and the structure below the penetration layer is still intact.These results demonstrate that ME(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta),especially ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),are promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking.