Effect of Aging on Hardening Behavior of 15-5 PH Stainless Steel

Microstructure transformation and aging hardening behavior of 15-5 PH stainless steel were studied by optical microscopy （OM）, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The results showed that the 15-5 PH stainless steel consists of NbC precipitates and lath matensite with a high dislocation density after solution treatment. With increasing aging temperature and aging time, the martensitic laths were resolved gradually. Meanwhile, the nanometric-sized Cu precipitates gradually coarsened and lost their coherency with＇the martensite matrix, which exhibited an elliptical shape finally. Fine Cu precipitates can lead to significant dispersion hardening effect, while the coarsened Cu precipitates have no contribution to strengthening. The reversed austenite was observed in the speci- mens aged at 550 ℃ and above; moreover, the amount of reversed austenite increased as aging temperature in- creased. The precipitation hardening behavior of 15-5 PH stainless steel may depend on the balance between the softening caused by the formation of reversed austenite and the hardening caused by the precipitation of copper.

Decorating graphdiyne on ultrathin bismuth subcarbonate nanosheets to promote CO_(2)electroreduction to formate

Electrocatalytic reduction of CO_(2)is one of the most attractive approaches for converting CO_(2)into valuable chemical feedstocks and fuels.This work reports a catalyst comprising graphdiyne-decorated bismuth subcarbonate(denoted as BOC@GDY)for efficient electroreduction of CO_(2)to formate.The BOC@GDY shows a stable current density of 200 mA cm^(-2)at–1.1 V in a flow cell configuration,with a faradaic efficiency of 93.5%for formate.Experimental results show that the synergistic effect in BOC@GDY is beneficial for the CO_(2)adsorption affinity,the reaction kinetics and the selectivity for formate.In addition,in-situ X-ray absorption and Raman spectroscopy indicate that the electron-rich GDY could facilitate the reduction from Bi(Ⅲ)to Bi(0),thus leading to more active sites.We also demonstrate that the promoting effect of GDY in CO_(2)electroreduction can be further extended to other metal catalysts.To the best of our knowledge,such general promoting functions of GDY for CO_(2)electroreduction have not been documented thus far.