Microstructure and mechanisms of fracture in corrosive enyironment in low precious metal for dental applications

采用不同热处理方法制备了低贵金属牙科用Ag-Pd-Cu-Au-Zn合金，研究了其静态、动态断裂韧性和拉伸性能。在相对较低的温度下固溶，然后风冷，即在1073 k下固溶3.6 k，然后风冷，我们发现，与一般推荐的热处理，即先固溶后时效相比，具有优异的断裂韧性和力学性能。在相对较低的温度下固溶，然后风冷，不仅可以有效地提高静态和动态断裂韧性，抗拉强度和伸长率，而且由于热处理过程中可以省去时效过程，是一种简单而低成本的热处理工艺。可以看出，传统的热处理方法并不总是适用于Ag-Pd-Cu-Au-Zn合金，因为在本研究中，除了评估拉伸性能外，还采用断裂韧性来评估Ag-Pd-Cu-Au-Zn合金的力学性能，这是迄今为止牙科领域唯一评估材料力学性能的方法。β相对Ag-Pd-Cu-Au-Zn型合金拉伸性能和断裂韧性的影响。在这种情况下，通过系统地改变β相的体积分数来评估拉伸性能和断裂韧性。到峰值时效阶段，随着β相体积分数的增加，强度增加，伸长率降低。固溶态合金在远离断口的地方观察到滑移带，而时效态合金仅在非常靠近断口的地方观察到滑移带。后一种现象可能是由于β相对滑移的限制，引起了局部变形。在时效条件下，当β相尺寸一定时，断裂韧性随β相体积分数的增加而降低；当β相体积分数一定时，断裂韧性随β相直径的减小而降低。然后，制备了不同Cu含量和不含Zn的实验合金。这些合金经过不同的热处理。然后，研究了Cu和Zn对Ag-Pd断裂韧性的影响。研究了-Cu-Au-Zn型合金。随着cu含量的增加，α_1相的体积分数增加，0.2%的抗拉应力降低，但由于加工硬化系数的增加，抗拉强度提高。加锌合金的强度和伸长率分别高于不加锌合金。在较高的温度下固溶Cu合金的静态断裂韧性相对较大。无锌合金的静态断裂韧性小于加锌合金。两种实验合金的力学性能均等于或大于工业合金。对Ag-Pd-Cu-Au-Zn型合金经不同热处理后的疲劳特性进行了研究，在水淬合金中，随着固溶温度的升高，α_2相的固溶强化在低周疲劳寿命区增强，疲劳强度增大。另一方面，在高周疲劳区，随着溶化温度的降低，α_1相的体积分数增加，α_1相实现了应变的释放，疲劳强度增大。然而，为了提高疲劳强度的绝对值，必须考虑β相的体积分数。在实际应用中，应对合金在口腔环境下的疲劳强度进行评价。因此，对经过不同热处理的合金在人工唾液中的疲劳特性进行了评价，并与在空气中的疲劳特性进行了比较。在低周疲劳寿命区，固溶态和时效态合金在空气和人工唾液中的疲劳强度基本相同。在高周疲劳寿命区，固溶态合金在空气和人工唾液中的疲劳强度基本相同，但时效合金在人工唾液中的疲劳强度小于在空气中的疲劳强度。在高周疲劳区，由于暴露于腐蚀环境的时间相对较长，β相与基体之间的界面优先被腐蚀。因此，在β相体积分数相对较大的时效合金中，腐蚀可能较为严重。腐蚀部位的应力集中可能相对较大。氯化物被认为是在这种腐蚀情况下由Cl和Ag反应形成的。铸造合金的断裂韧性研究具有重要的意义，因为铸造产品一般都是实际使用的。研究了不同热处理条件下Ag-Pd-Cu-Au-Zn型铸造合金的断裂行为。铸态合金的抗拉强度趋于小于变形合金。然而，在1073 K固溶处理后，与变形合金相比，铸态合金的抗拉强度下降很小。结果表明：1073 K固溶+空冷的处理方法对铸态合金较为适宜。研究了Ag-Pd-Cu-Au-Zn型合金在人工唾液中的摩擦磨损特性。时效合金摩擦磨损失重最小，析出的β相体积分数相对较大。在1123 K固溶后以α_2单相水淬的合金与在1073 K固溶后以α_1单相水淬的合金具有相同的摩擦磨损损失。阶段。1073 K固溶时效合金和1123 K水淬合金的摩擦磨损损失最小，而1123 K固溶时效合金的摩擦磨损损失最大。试件与配合销之间的摩擦系数与试件与配合销的摩擦磨损失重有关。少

Low precious dental Ag-Pd-Cu-Au-Zn type alloys were conducted with various heat treatments, and then their static and dynamic fracture toughness, and tensile properties were investigated. Solutinizing at relatively lower temperature followed by air cooling, that is, solutionized at 1073 k for 3.6 ks followed by air cooling, we found to exhibit excellent fracture toughness and mechanical properties comparing with generally recommended heat treatment, that is, solutionizing followed by aging. Solutionizing at relatively lower temperature followed by air cooling is not only effective to improve static and dynamic fracture toughness, and tensile strength and elongation, but also simple and low cost heat treatment process because aging process can be omitted during heat treatment process. It was possible to point out that the conventional heat treatment was not always suitable for Ag-Pd-Cu-Au-Zn type alloy because in this study fracture toughness was adopted for evaluating the mechanical pe … More rformance of Ag-Pd-Cu-Au-Zn type alloy in addition to the evaluation of tensile properties, which was the only method for evaluating the mechanical performance of the materials in the dental field to date.The effect of β phase on the tensile properties and fracture toughness of Ag-Pd-Cu-Au-Zn type alloy. In that case, tensile properties and fracture toughness were evaluated with systematically changing the volume fraction of β phase. Up to the peak age condition, strength increased and elongation decreased with increasing the volume fraction of β phase. Slip bands were observed on the part far from the fracture surface for the as-solutionized alloy, but only very near the fracture surface for the aged alloy. The latter phenomenon could be due to the restriction of slip by β phase, which caused the local deformation. In the under age condition, fracture toughness decreased with increasing the volume fraction of β phase when the size of β phase was constant, while fracture toughness decreased with decreasing the diameter of β phase when the volume fraction of β phase was constant.Then, the experimental alloys with varying Cu content and without Zn were fabricated. These alloys were variously heat-treated. Then, the effects of Cu and Zn on the fracture toughness of Ag-Pd.-Cu-Au-Zn type alloy were investigated. Since the volume fraction of α_1 phase increased with increasing cu content, 0.2% proof stress decreased, but tensile strength increased due to increasing work hardering coefficient. The strength and elongation of Zn added alloy were greater and smaller, respectively comparing with Zn free alloy. The static fracture toughness of Cu added alloy was relatively greater through solutionizing at relatively higher temperature. the static fracture toughness of Zn free alloy was smaller than that of Zn added alloy. The mechanical properties of both experimental alloys were found to be equal to or greater than those of commercial alloy.The fatigue characteristics of Ag-Pd-Cu-Au-Zn type alloy conducted with various heat treatments were then investigated in the case of water quenched alloy, fatigue strength was greater with increasing solutionizing temperature because solid solution strengthening of α_2 phase increased in the low cycle fatigue life region. On the other hand, in the high cycle fatigue region, the fatigue strength was greater with decreasing solutionizing temperature because the volume fraction of α_1 phase increased and strain relief was achieved by α_1 phase. However, the volume fraction of β phase was necessary to be taken into ccount in order to increase the absolute value of fatigue strength. For the practical use of the alloy, the fatigue strength should be evaluated in the oral *nyironment. Therefore, the fatigue characteristics of the alloys conducted with various heat treatments were evaluated in the artificial saliva, and compared with those evaluated in air. The fatigue strength of as-solutinized and aged alloys was nearly the same in air and artificial saliva in the low cycle fatigue life region. In the high cycle fatigue life region, the fatigue strength of as-solutionized alloy was nearly the same in air and artificial saliva, but the fatigue strength of aged alloy was smaller in artificial saliva than in air. In the high cycle fatigue region, since the exposure time to corrosion environment was relatively longer, and the interface between β phase and matrix was preferentially corroded. Therefore, the corrosion might be severe in the aged alloy where the voltume fraction of β phase was relatively greater. The stress concentration to the corroded parts might be relatively greater. Chloride was considered to form by the reaction of Cl with Ag in this case of corrosion.It was important to investigate the fracture toughness of cast alloys because casting products were in general practically used. Fracture behavior of cast Ag-Pd-Cu-Au-Zn type alloys conducted with various heat treatments were investigated. Tensile strength of the cast alloy tended to be smaller than that of the wrought alloy. However, a decrcase in tensile strength of the cast alloy comparing with the wrought alloy was little when solution treatment was done at 1073 K followed by air-cooling. The neat treatment of solutionizing at 1073 K followed by air-cooling was judged to be proper for the cast alloy.Friction wear characteristics of Ag-Pd-Cu-Au-Zn type alloy was investigated in artificial saliva. Friction wear weight loss was the smallest in aged alloy where the volume fraction of precipitated β phase was relatively greater. The alloy solutionized at 1123 K followed by water quenching with single α_2 phase exhibit the same friction wear weight loss as that of the alloy solutionized at 1073 K followed by water quenching with α_1. phase. Friction wear weight loss of mating pin made of this alloy against the alloy conducted with solutionizing and aging was the smallest Friction wear loss of the alloys solutionized at 1073 K and 1123 K followed by water quenching was greater than that of the alloy conducted with solutionizing and aging, and was the greatest for the alloy conducted with solutionizing at 1123 K followed by water quenching. Friction coefficient between specimen and mating pin was found to relate with the friction wear weight loss of the specimen and mating pin. Less