The Studies On Synthesis Of Cr₂AlC Ceramic Powders And Fabricate The Bulk

Cr₂AlC is the Mn+1AXn（n=1,2,3） phase of the layered-ternary compounds, whichbelongs to hexagonal systems.It has excellent thermal conductivity and high conductivitysimilar to the metal, but also has more good thermal shock resistance.And it has highstrength,high modulus,shear modulus of elasticity,corrosion resistance and good oxidationresistance similar to ceramics.Excellent performance determines its wide range ofapplications,so it started to pay attention by more and more scholars.Using Cr,Al and Cpowders（Cr:Al:C=2:1.2:1,mol%）as the reaction raw materials, Cr₂AlC ceramics weresynthesized under the700～1450℃.Material characteristic temperatures during the thermalreaction were defined by Differential thermal analysis （DTA）, phase composition of reactionproducts were analyzed by X-ray diffraction （XRD） and microstructure of reaction productswere analyzed by Scanning electron microscopy（SEM）.The results shows that the mainproducts consist of Cr₉Al₁₇,Cr₅Al₈and Cr2Al phases in the range of700～1250℃.Between1250℃and1350℃,single phase Cr₂AlC with small amount of Cr₇C₃are produced,andCr₂AlC increase the amount of which increase with temperature.Up to1450℃,the amount oftarget product Cr₂AlC phase becomes less,instead of the increasing Cr₇C₃phase.Based on theanalysis results speculate that the reaction mechanism during Cr₂AlC reaction.Study theimpact of the initial ratio of raw materials graphite content and aluminum content, and preparepure Cr₂AlC material when the Cr:Al:C=2:1.2:0.93.In addition, we study the added titaniumand using titanium substituted chromium prepare Cr₂AlC solid solution formation reaction,when the ratio of raw materials were n（Cr）:n（Ti）:n（Al）:n（C）=2:0.1:1.2:1and n（Cr）:n（Ti）:n（Al）:n（C）=1.95:0.05:1.2:1both prepared high purity Cr₂AlC solid solution. Studyconductivity and thermal stability of the results showed that impurities impact on theconductivity of samples and Cr₂AlC samples has very good antioxidant capacity under900℃.For n（Cr）:n（Al）:n（C）=2:1.2:1,hot-pressing at1350℃for1h,pressure were15MPa,20MPa,25MPa prepared Cr₂AlC bulk.Study shows that the greater the pressure,the greater its density,bending strength,but the smaller Vickers hardness.15MPa and20MPa by hot-pressing of theCr₂AlC bulk thermal expansion is small, stable at1.5×10²μm to4.0×10²μm，shows thatCr₂AlC bulk materials have good thermal stability.Study chemical corrosion of the conditions of15MPa by hot-pressing the Cr₂AlC bluk shows that,Cr2A1C bulk materials resistance basicmaterials much better than the acid materials.So the Cr2A1C material should avoid acidicenvironment contact as much as possible,particularly hydrochloric acid during the practicalapplication.