Experimental Research On Indentation Test Of Single Crystal Copper At Low Temperature

At present,various scientific research and numerous industrial fields are gradually involved in low temperature environment,and cryogenic temperature is also one of the important factors affecting the mechanical properties of materials.Single crystal copper is a high purity copper with a purity of 99.9999%.Its excellent plastic processing,fatigue resistance,corrosion resistance and signal transmission performance are the most suitable and excellent materials for making micromachines and micro-components,and in aerospace and superconductor.It is widely used in low temperature environments such as guiding technology and polar scientific research.Therefore,the low temperature nanoindentation test of single crystal copper is also very important to research the change of mechanical properties.Based on the current research status of low temperature nanoindentation test technology and microscopic mechanical properties of crystalline copper,this paper proposes a low temperature indentation test of single crystal copper by self-made low temperature nanoindenter,through indentation curve and indentation shape.The effect of low temperature environment on the mechanical properties of single crystal copper was analyzed.Before the formal test,the Oliver-Pharr micro-nano indentation test theory was first analyzed,and the low-temperature nano indentation instrument made by the research group was briefly introduced.The force sensor and displacement sensor were calibrated,and the load and displacement of the instrument were applied.Calibration with rack compliance allows the calibrated instrument to be tested with commercial indenters.The calibrated instrument has good repeatability and accuracy,and the obtained indentation curve of the standard fused silica specimen has high repeatability with the standard curve obtained by the commercial indenter,wherein the hardness deviation is 0.87%.The modulus of elasticity deviation was 1.7%.According to the characteristics of cooling mode,the method of reducing the temperature difference between the indenter and the test piece is proposed to improve the temperature drift.The improved temperature drift value is h ?0.01?m,the influence is greatly weakened,and the accuracy of the test result is improved.The effect of temperature on the mechanical properties of single crystal copper was investigated by performing low temperature nano-indentation test on single crystal copper and deeply analyzing the change of load-depth curve.The results show that in the temperature range of 300K~150K,the indentation hardness and elastic modulus of single crystal copper increase with the decrease of temperature,and the lower the temperature,the faster the increase in the hardness and modulus of elasticity of the single crystal copper.The hardness and elastic modulus of the three crystal faces of the single crystal copper at the same temperature are(111)>(110)>(100).At the same time,using MATLAB software to calculate the elastic-plastic energy of single crystal copper in low temperature nano-indentation test.In the temperature range of 300K~150K,the elastic recovery energy and plastic deformation energy of single crystal copper decrease with the decrease of temperature.At the same temperature,the relationship between the elastic recovery energy and the plastic deformation energy of three crystal plane single crystal copper is(100)>(110)>(111).The elastic deformation energy has a correlation with the elastic modulus,and the rate of decrease with the decrease of the temperature is faster.The plastic deformation energy has a correlation with the indentation hardness,and the slower the rate of decrease with the decrease of temperature,the temperature change affects the mechanical properties of single crystal copper more or less.The surface morphology of single crystal copper indentation was analyzed by scanning electron microscopy.The influence of temperature on the indentation response and deformation mechanism of single crystal copper was investigated.The results show that in the temperature range of 300K~150K,the lower the temperature,the more obvious the slip zone generated by the plastic deformation of single crysta l copper on the surface of the indentation.The stronger the ability of the atom inside the crystal to resist deformation,the more difficult it is to plastically deform.The lower the temperature,the weaker the ability of the plastic deformation of the s ingle crystal copper to expand outward at the boundary of the indentation surface,and the stronger the ability to recover elastic.At the same time,it was found that single crystal copper produced pile-up during the sliding process,that is,the accumula tion phenomenon,and the single crystal copper of the(100)crystal plane was piled up along the <110> direction,and the deposition decreased with temperature.It is less and less obvious.According to the different crystal planes of single crystal,the test phenomena of different indentation morphology and different deformation directions,it is proved that the anisotropy of plastic deformation of single crystal copper is related to the orientation of crystal plane,which is caused by the difference of cr ystal planes,resulting in slippage.Different directions,showing the difference in plastic deformation,independent of temperature.