Impact Analysis of Microscopic Defect Types on the Macroscopic Crack Propagation in Sintered Silver Nanoparticles

Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure.Component distribution Ni（75）AlxV（25-x） alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition,precipitate order,precipitate type,and phase stability.The Ni（75）AlxV（25-x） alloys undergo single Ni3V（stage Ⅰ）,dual Ni3Al and Ni3V（stage Ⅱ with Ni3V prior;and stage Ⅲ with Ni3Al prior）,and single Ni3Al（stage Ⅳ） with enhanced aluminum level.For Ni3V phase,anti-structured defects（V（Ni1）,Niy,except V（Ni2）） and substitution defects（Al（Ni1）,Al（Ni2）,Alv） exhibit a positive correlation to aluminum in stage I,the positive trend becomes to negative correlation or smooth during stage Ⅱ.For Ni3 Al phase,anti-structured defects（Al（Ni）,Ni（Al）） and substitution defects（V（Ni）,V（Al）） have a positive correlation to aluminum in stage Ⅱ,but Ni（Al） goes down since stage Ⅲ and lasts to stage Ⅳ.V（Ni） and V（Al） fluctuate when Ni3Al precipitates prior,but go down drastically in stageⅣ.Precipitate type conversion of single Ni3V/dual（Ni3V＋Ni3Al） affects Ni3V defects,while dual（Ni3V＋Ni3Al）/single Ni3 Al has little effect on Ni3Al defects.Precipitate order swap occurred in the dual phase region affects on Ni3Al defects but not on Ni3V.

Experimental investigation of axial tensile and fatigue behaviors of HTS round strands

For the development of high‐temperature superconducting(HTS)magnet systems of future fusion devices,a novel HTS round strand based on a stacking structure was designed and manufactured using second generation(2G)HTS tapes.Different mechanical loads during operation can result in irreversible degradation of the strand.The axial tension and fatigue loads need particular attention.Therefore,it is important to investigate the electromechanical behavior of the round strand under various axial tension and cyclic loads.In this paper,the axial tensile and fatigue tests were conducted at 77 K,self‐field.Taking 95%critical current(I_(c))retention as the criterion,the results of the tensile tests revealed that the average tensile stress and strain were as high as 344 MPa and 0.47%,respectively.Fatigue characteristics were also investigated as a function of axial tensile stress.No significant performance degradation was observed up to 100,000 loading cycles with stress amplitudes ranging from 20 MPa to 200 MPa.Ic degradation occurs after 16,000 loading cycles with 380 MPa as the maximum stress.Furthermore,the microscopic defects of the round strand samples due to fabrication imperfections and mechanical loading were investigated using metallographic microscope and scanning electron microscope.These results presented in this paper are useful for comprehending and improving the mechanical behaviors of the strand in high‐field and large‐scale fusion magnet systems.