The Effect Of Cryogenic Treatment On The Mechanic Characteristics Of The Co-Cr Alloy

Cobalt-chromium(Co-Cr)alloy is currently widely exploited in prosthodontical field because of its light density,cheap price and high biocompatibility.However,Co-Cr alloy has some disadvantages while used in the complicated active oral environment.For example,the clasp and connecter of removable partial denture will be fractured,and the crowns and bridges will be broken down after a period of time.Cryogenic treatment is a common method used in industry area,which can improve the mechanic characteristics of several metals.So,if the mechanical properties of Co-Cr alloy could be enhanced by cryogenic treatment,the lifetime of prosthetic replacements would be extended.In this study,the Co-Cr alloy was treated by cryogenic treatment, and the effects on the dimension,hardness,wear resistance and bending strength of this material were examined.PartⅠ.The Effect of Cryogenic Treatment on the Dimension of the Co-Cr AlloyObjective:To investigate the effects of cryogenic treatment on the dimension of the Co-Cr alloy.Materials and methods:15 samples were divided into three groups, including fast cryogenic treatment group,slow cryogenic treatment and cycle slow cryogenic treatment group.Each group has 5 samples.A vernier caliper was used to examine the length,width and thickness of the samples.Results:The dimensions of the samples after fast cryogenic treatment were changed remarkably(P＜0.05).There was no difference between slow cryogenic treatment group and cycle slow cryogenic treatment group(P＞0.05).Conclusion:The slow cryogenic treatment and cycle slow cryogenic treatment couldn't create obvious deformation of the Co-Cr alloy.PartⅡ.The Effect of Cryogenic Treatment on the Hardness and the Wear Resistance of the Co-Cr AlloyObjective:To investigate the effects of cryogenic treatment on the hardness and the wear resistance of the Co-Cr alloy.Materials and methods:20 samples were divided into four groups, including the control group(C),the cryogenic treatment group(E1),cryogenic treatment plus tempering treatment group(E2)and cycle cryogenic plus tempering treatment group(E3).Each group has 5 samples.A Vicker's intender was used to examine the hardness of the samples.Weight loss measurement under the conditions of scratching and the rate of weight loss under the conditions of rolling were used to examine the wear resistance.Results:The Vicker's hardness of group E1 and group E3 were higher than that of group C(P＜0.05).There was no difference among group E1,group E2,group E3 and group C(P＞0.05).The rate of weight loss of group E3 after rolling abrasion was lower than that of group C(P＜0.05).Conclusion:The results suggested that the hardness and wear resistance of the Co-Cr alloy could be matched well by proper cryogenic treatment.PartⅢ.The Effect of Cryogenic Treatment on the bending strength of the Co-Cr AlloyObjective:To investigate the effects of cryogenic treatment on the bending strength of the Co-Cr alloy.Materials and methods:10 samples were divided into two groups, including the control group and cycle cryogenic plus tempering treatment group.Each group has 5 samples.A universal testing machine was used to examine the bending strength of the samples.SEM images were used to analyze the mechanism that improved the bending strength of the alloy.Results:For Co-Cr alloy the bending strength was effectively increased after cycle cryogenic plus tempering treatment(P＜0.05).The SEM images showed that the cartridge area changed into symmetry area,and more tiny carbonide separated out all over the alloy.Conclusion:The results suggested that the bending strength of the Co-Cr alloy could be improved by cycle cryogenic plus tempering treatment.