DEVELOPMENT OF CRYOGENIC HARDINESS TESTER AND FRICTION TESTER AT CRYOGENIC TEMPERATURE

本文研制了一种新型的维氏型低温硬度计。旧的用液氦冷却，但由于液氦的蒸发，温度和升温速率无法控制。因此，我们引入了一种转基因冰箱，在真空室中进行控制。硬度计的性能是合格的。问题是不能在4 K左右冷却样品，因为冰箱的第二冷却阶段头部和样品的传导接触电阻。在这个测试中，温度在30k左右被冷却。我们不仅测量了SUS316L不锈钢等金属试样的硬度，还测量了高温超导体YBCO、（Nd,Eu,Gd）BaCuO等材料的硬度。后者被用作体磁铁，但它在磁化过程中容易受到洛伦兹力的破坏。断裂韧性K_<IC>由硬度和硬度试验中由压痕产生的裂纹尺寸来评定。总体上，硬度随温度的降低单调增加，且分散性较大，而断裂韧性随温度的升高略有下降。例如，（Nd,Eu,Gd）BaCuO在40 K时的硬度为9800 MPa。断裂韧性取决于晶面，因为晶面上存在许多固有裂纹，裂纹更容易扩展。我们还配备了在腔室中具有往复滑动运动的销台式摩擦测试仪。试样的温度在40 K到室温范围内有效。遗憾的是，由于时间有限，我们无法获得摩擦日期。在40 K和室温条件下测试了摩擦试验机的性能，结果令人满意。稍后，我们将得到材料的摩擦系数与温度的关系。

In this work we developed the new Vickers-type cryogenic hardness tester, using GM-refrigerator. The old one was cooled with liquid helium, but the temperature and temperature rising rate could not be controlled because of the evaporation of liquid helium. Therefore, we introduced a GM-refrigerator to control in a vacuum chamber. The performance of the hardness tester was acceptable. The problem was not to cool a specimen at around 4 K due to the contact resistance of conduction from the second cooling stage head of the refrigerator and the specimen. The temperature was cooled down at around 30 K in this tester.We measured the hardness not only metallic specimens such as SUS316L stainless steel, but also high temperature superconductors such as YBCO, and ((Nd,Eu,Gd)BaCuO). The latter was used as the bulk magnet, but it breaks down easily with Lorentz force during magnetizing. The fracture toughness K_<IC> was evaluated from the hardness and the crack size initiated from an indented scar during hardness test. Generally, hardness was increased with decreasing temperature monotonically with rather great scatter, but the fracture toughness was slightly decreased with temperature. For example, the hardness of (Nd,Eu,Gd)BaCuO was 9,800 MPa at 40 K. The fracture toughness depends on the crystal plane because there were many inherent cracks on the (100) plane and it was easier for cracks to propagate.We also equipped the pin-on-desk type friction tester with a reciprocating sliding motion in the chamber. The temperature of the specimen was valid from 40 K to room temperature. Unfortunately, we could not obtain the frictional date due to lack of time. The performance of the frictional tester was examined at 40 K and room temperature, and we are satisfied. Later, we will obtain the temperature dependence of coefficient of friction of materials.