Molecular Dynamics Study On The Effect Mechanism Of Hydrogen Atoms On Crack Propagation In Fe-Ni Alloys

In nature,hydrogen can easily enter to metal materials,resulting a reduction in the mechanical properties of metal materials and inducing brittle failures,also known as hydrogen embrittlement.In industry,the failure of metal materials due to hydrogen embrittlement will cause significant property damage and life hazards.Therefore,the study of hydrogen embrittlement has always been a concern in the academic community.At present,many mechanisms have been proposed for hydrogen embrittlement mechanism,such as HP,HELP,HID,etc.However,different mechanisms all have certain limitations.Therefore,the exact mechanism of hydrogen embrittlement is still quite different in the academic community.There are many factors can effect the metal property of hydrogen embrittlement resistance.Some researchers improved metal property against hydrogen embrittlement by adjusting alloy compositions,such as introducing Ni element into alloys.Exploring the effect mechanism of Ni element to alloy crack tip extension process is important for high hydrogen embrittlement resistance property material research and development.Under the existing experimental conditions and methods,it is difficult to truly track the occurrence of hydrogen embrittlement.However,the use of molecular dynamics simulation which based on modified embedded atom method facilitates a fundamental understanding of the interaction between hydrogen and metal.Therefore,the new Fe-NiH potential was confirmed.And this potential was used to simulate the tensile process of pre-crack Fe-Ni system under different Ni content and H content by MD method,in order to study the effect mechanism of Ni and H element to alloy crack extension and mechanical property.After that,we discussed how the effect of H element change under different Ni content.With the increasing of alloy Ni content,Fe-Ni system crystal structure will change from BCC to FCC.Ni element can enhance the Fe-Ni system FCC phase stability.With the increasing of Ni content,the plasticity and hydrogen embrittlement resistance property will increase firstly and then decrease.The reason is that the Fe-Ni system with Ni content of 20 at% has a better plasticity compared with pure Fe system so the stress concentration is difficult to happen,and in the Fe-Ni system with Ni content more than 20 at% the Ni element will bring stronger blocking to stacking fault so the stress near crack tip is difficult to be defused.The higher hydrogen concentration could promote the stress concentration near crack tip,enhance crack extension and cause the Fe-Ni system having higher tensile strength.That was caused by the hinder effect of hydrogen to stacking fault and phase transformation in tensile process.As the Ni content increase,the effects caused by hydrogen to Fe-Ni system decrease.