Amelioration of weld-crack resistance of the M951 superalloy by engineering grain boundaries

Fusion weld is a portable and economical joining and repairing method of metals.However,weld cracks often occur during the fusion weld of Ni-base superalloys,which hinder the applications of fusion weld on this kind of materials.In this work,the effects of microstructures of grain boundaries(GBs)of the prototype M951 superalloy on its weldability were investigated.The precipitated phases,the elemental segregations on GBs,and the morphologies of GBs can be largely altered by regulating the cooling rates of pre-weld heat treatments.With decreasing the cooling rate,chain-like M_(23)X_(6)phase precipitates along the GBs,accompanying segregations of B,and GBs becomes more serrated in morphology.During fusion weld,the engineered GBs in the M951 superalloy with a low cooling rate favor the formation of the continuous liquid films on GBs,which together with the serrated GB morphology significantly prevents the formation of weld cracks.Our findings imply that the weld-crack resistance of the superalloys can be ameliorated by engineering GBs.

A stretchable and adhesive ionic conductor based on polyacrylic acid and deep eutectic solvents

Hydrogels are a widely used ionic conductor in on-skin electronic and iontronic devices.However,hydrogels dehydrate in the open air and freeze at low temperatures,limiting their real applications when they are attached on skin or exposed to low temperatures.Polymer-ionic liquid gels can overcome these two obstacles,but synthetic ionic liquids are expensive and toxic.In this work,we present an ionic conductor based on polyacrylic acid(PAAc)and deep eutectic solvents(DESs)that well addresses the aforementioned challenges.We polymerize acrylic acid in DESs to get the PAAc–DES gel,which exhibits excellent stretchability(>1000%),high electrical conductivity(1.26 mS cm^(−1)),high adhesion to the skin(~100 Nm^(−1)),as well as good anti-drying and anti-freezing properties.We also demonstrate that the PAAc-DES gel can be used as an on-skin electrode to record the surface electromyographic signal with high signal quality,or as a transparent stretchable electrode in iontronic devices that can work at–20℃.We believe that the PAAc–DES gels are an ideal candidate as epidermal electrodes or transparent stretchable electrodes.