Mechanical properties and deformation mechanisms of surface-modified 6H-silicon carbide

The effect of amorphous film on the deformation mechanism and mechanical properties of 6 H-SiC were systematically explored by a combination of both experiments and molecular dynamic(MD)simulations in nanoindentation.The experimental results showed that the plastic deformation of surface-modified6 H-SiC is mainly accommodated by dislocation activities in the subsurface and an amorphous layer with uniform thickness.The MD results indicated that the amorphous layer on the surface of the residual indentation mark consists of both amorphous SiO_(2)and SiC due to direct amorphization.In addition,the amorphous SiO_(2)film undergoes densification and then ruptures with the indentation depth increases.The modulus and hardness increase with increasing the indentation depth at the initial stage but will reach their stable values equivalent to monocrystalline 6 H-SiC.

A data-driven approach to RUL prediction of tools

An effective and reliable prediction of the remaining useful life(RUL)of a tool is important to a metal forming process because it can significantly reduce unexpected maintenance,avoid machine shutdowns and increase system stability.This study proposes a new data-driven approach to the RUL prediction for metal forming processes under multiple contact sliding conditions.The data-driven approach took advantage of bidirectional long short-term memory(BLSTM)and convolutional neural networks(CNN).A pre-trained lightweight CNN-based network,WearNet,was re-trained to classify the wear states of workpiece surfaces with a high accuracy,then the classification results were passed into a BLSTM-based regression model as inputs for RUL estimation.The experimental results demonstrated that this approach was able to predict the RUL values with a small error(below 5%)and a low root mean square error(RMSE)(around 1.5),which was more superior and robust than the other state-of-the-art methods.

Superior high-temperature wear resistance of an Ir-Ta-Ni-Nb bulk metallic glass

Wear resistance is a critical consideration in engineering applications.In this study,we demonstrated an Ir-Ta-Ni-Nb bulk metallic glass(BMG)with outstanding high-temperature wear resistance and revealed its promising applications in extreme environments.The wear behavior and mechanism were systemati-cally investigated from room temperature(RT)to 750℃.The results show that the wear rate increases from∼2.65×10^(-6)mm^(3)N^(-1)m^(-1)to∼10.56×10^(-6)mm^(3)N^(-1)m^(-1)in the temperature span RT to 400℃,following abrasive wear and flash temperature-induced oxidative wear during the friction.However,at the higher temperature of 600℃,further heating due to frictional heat leads to a softening of the wear surface,resulting in a maximum wear rate of∼20.99×10^(-6)mm^(3)N^(-1)m^(-1)under softness-driven abrasive wear as well as oxidative wear.Interestingly,the wear resistance at an even higher temperature of 750℃shows a paradoxical improvement of∼7.08×10^(-6)mm^(3)N^(-1)m^(-1),which is attributed to the formation of an oxide layer with a thickness of several microns,avoiding violent wear of BMG.The re-sults demonstrate the unreported outstanding high-temperature wear resistance of the Ir-Ta-Ni-Nb BMG,especially its excellent capability to resist wear at 750℃,leading to the promising applications of BMG in the fields of aerospace,metallurgy,and nuclear industries.

Debris effect on the surface wear and damage evolution of counterpart materials subjected to contact sliding

This paper aims to explore the debris effect on surface wear and damage evolution of counterpart materials during contact sliding.A cylinder-on-flat testing configuration is used to investigate the wear behaviours of the contact pair.To explore the roles of wear debris,compressed air is applied to remove the debris in sliding zones.The comparative study demonstrates that the influence of debris removal is related to the surface properties of contact pairs.When substantial wear debris accumulates on the tool surface,debris removal can considerably alter surface damage evolution,resulting in different friction transitions,distinct surface morphology of contact pair,as well as different rates of material removal.It has been found that the surface damage evolution will not reach a stable stage unless the increase of wear particle number ceases or the average size of wear particles becomes lower than a specific threshold.However,the influence of debris removal reduces when the adhesion between the contact pair materials gets smaller.

An analytical method for assessing the initiation and interaction of cracks in fused silica subjected to contact sliding

Understanding the fracture behavior of fused silica in contact sliding is important to the fabrication of damage-free optics.This study develops an analytical method to characterize the stress field in fused silica under contact sliding by extending the embedded center of dilation(ECD)model and considering the depth of yield region.The effects of densification on the stress fields were considered by scratch volume analysis and finite element analysis.Key mechanisms,such as crack initiation and morphology evolution were comprehensively investigated by analyzing the predicted stress fields and principal stress trajectories.The predictions were validated by Berkovich scratching experiment.It was found that partial conical,median and lateral cracks could emerge in the loading stage of the contact sliding,but radial and lateral cracks could be initiated during unloading.It was also found that the partial conical crack had the lowest initiation load.The intersection of long lateral cracks makes the material removal greater.