The precipitation process of zirconium hydrides induced by stress and strain was investigated by means of electron microscopy in-situ.The precipitating hydrides induced by stress were found to be γ phase with orienta...The precipitation process of zirconium hydrides induced by stress and strain was investigated by means of electron microscopy in-situ.The precipitating hydrides induced by stress were found to be γ phase with orientation relationship of (110)_γ‖(110)_(αZr),(001)_γ‖ (0001)_(αZr) between γ-hydrides and surrounding matrix.The growth rate of γ-hydrides which was much faster along [110] direction brought them in taper shape.After fracture of y-hydrides,a new one will precipitate at the tip of cracks.This is the essential process of hydrogen-induced delayed cracking in Zircaloy.The precipitating hydrides induced by strain were found to be δ phase with both orientation relationships of(111)_δ‖(0001)_(αZr),(110)_δ‖ (110)_(αZr) or (010)_δ‖(0001)_(αZr),(001)_δ‖(110)_(αZr)between δ-hydride and surrounding matrix.The δ-hydrides become much finer as the strain rate increased.展开更多
Cracks and fractures occur during the assembly process to a type of torsional springs used in the aviation mechanism. Besides visual examination, other experimental techniques used for the investigation are： 1） frac...Cracks and fractures occur during the assembly process to a type of torsional springs used in the aviation mechanism. Besides visual examination, other experimental techniques used for the investigation are： 1） fracture characteristics, damage morphology and fractography by scanning electron microscopy （SEM）, 2） spectrum analysis of covering, 3） metallographic observation of cracks and 4） hydrogen content testing. The results are obtained through the analysis of manufacture process and experimental data. Since no changes of microstructure are found, failures are irrelevant to the material. The cracks and fractures initiate on the inner surface, cracks initiate before the cadmium plating and after the winding. No obvious stress corrosion cracks are found near the crack source region. The opening direction of cracks is consistent with the residual tensile stress of the spring inner surface, and the springs are easy to contact hydrogen media between the spring winding and the cadmium plating. The cracks are caused by hydrogen-induced delayed cracking under the action of the residual tensile stress and hydrogen.展开更多
The hydrogen embrittlement(HE)fracture of advanced high-strength steels used in lightweight automobiles has received increasing public attention.The source,transmission,and movement of hydrogen,characterization parame...The hydrogen embrittlement(HE)fracture of advanced high-strength steels used in lightweight automobiles has received increasing public attention.The source,transmission,and movement of hydrogen,characterization parameters,and test methods of HE,as well as the characteristics and path of HE fractures,are introduced.The mechanisms and modes of crack propagation of HE and hydrogen-induced delayed fracture are reviewed.The recent progress surrounding micro and macro typical fracture characteristics and the influencing factors of HE are discussed.Finally,methods for improving HE resistance can be summarized as follows:(1)reducing crystalline grain and inclusion sizes(oxides,sulfides,and titanium nitride),(2)controlling nano-precipitates(niobium carbide,titanium carbide,and composite precipitation),and(3)increasing residual austenite content under the reasonable tension strength of steel.展开更多
文摘The precipitation process of zirconium hydrides induced by stress and strain was investigated by means of electron microscopy in-situ.The precipitating hydrides induced by stress were found to be γ phase with orientation relationship of (110)_γ‖(110)_(αZr),(001)_γ‖ (0001)_(αZr) between γ-hydrides and surrounding matrix.The growth rate of γ-hydrides which was much faster along [110] direction brought them in taper shape.After fracture of y-hydrides,a new one will precipitate at the tip of cracks.This is the essential process of hydrogen-induced delayed cracking in Zircaloy.The precipitating hydrides induced by strain were found to be δ phase with both orientation relationships of(111)_δ‖(0001)_(αZr),(110)_δ‖ (110)_(αZr) or (010)_δ‖(0001)_(αZr),(001)_δ‖(110)_(αZr)between δ-hydride and surrounding matrix.The δ-hydrides become much finer as the strain rate increased.
文摘Cracks and fractures occur during the assembly process to a type of torsional springs used in the aviation mechanism. Besides visual examination, other experimental techniques used for the investigation are： 1） fracture characteristics, damage morphology and fractography by scanning electron microscopy （SEM）, 2） spectrum analysis of covering, 3） metallographic observation of cracks and 4） hydrogen content testing. The results are obtained through the analysis of manufacture process and experimental data. Since no changes of microstructure are found, failures are irrelevant to the material. The cracks and fractures initiate on the inner surface, cracks initiate before the cadmium plating and after the winding. No obvious stress corrosion cracks are found near the crack source region. The opening direction of cracks is consistent with the residual tensile stress of the spring inner surface, and the springs are easy to contact hydrogen media between the spring winding and the cadmium plating. The cracks are caused by hydrogen-induced delayed cracking under the action of the residual tensile stress and hydrogen.
基金This work was financially supported by the State Key Laboratory of Vehicle NVH and Safety Technology(NVHSKL-202104)the innovation research group of universities in Chongqing(CXQT21030,CXQT19031).
文摘The hydrogen embrittlement(HE)fracture of advanced high-strength steels used in lightweight automobiles has received increasing public attention.The source,transmission,and movement of hydrogen,characterization parameters,and test methods of HE,as well as the characteristics and path of HE fractures,are introduced.The mechanisms and modes of crack propagation of HE and hydrogen-induced delayed fracture are reviewed.The recent progress surrounding micro and macro typical fracture characteristics and the influencing factors of HE are discussed.Finally,methods for improving HE resistance can be summarized as follows:(1)reducing crystalline grain and inclusion sizes(oxides,sulfides,and titanium nitride),(2)controlling nano-precipitates(niobium carbide,titanium carbide,and composite precipitation),and(3)increasing residual austenite content under the reasonable tension strength of steel.
