Grain boundary engineering for enhancing intergranular damage resistance of ferritic/martensitic steel P92

Ferritic/martensitic(F/M)steel is widely used as a structural material in thermal and nuclear power plants.However,it is susceptible to intergranular damage,which is a critical issue,under service conditions.In this study,to improve the resistance to intergranular damage of F/M steel,a thermomechanical process(TMP)was employed to achieve a grain boundary engineering(GBE)microstructure in F/M steel P92.The TMP,including cold-rolling thickness reduction of 6%,9%,and 12%,followed by austenitization at 1323 K for 40 min and tempering at 1053 K for 45 min,was applied to the as-received(AR)P92 steel.The prior austenite grain(PAG)size,prior austenite grain boundary character distribution(GBCD),and connectivity of prior austenite grain boundaries(PAGBs)were investigated.Compared to the AR specimen,the PAG size did not change significantly.The fraction of coincident site lattice boundaries(CSLBs,3≤Σ≤29)and Σ3^(n) boundaries along PAGBs decreased with increasing reduction ratio because the recrystallization fraction increased with increasing reduction ratio.The PAGB connectivity of the 6%deformed specimen slightly deteriorated compared with that of the AR specimen.Moreover,potentiodynamic polarization studies revealed that the intergranular damage resistance of the studied steel could be improved by increasing the fraction of CSLBs along the PAGBs,indicating that the TMP,which involves low deformation,could enhance the intergranular damage resistance.

Retarding the precipitation of η phase in Fe-Ni based alloy through grain boundary engineering

It is important to inhibit the precipitation of η phases in precipitation strengthened Fe-Ni based alloys,as they will deteriorate not only the mechanical property but also the hydrogen resistance.The present investigation shows that grain boundary engineering(GBE) can retard the formation and growth of ηphase in J75 alloy.After GBE treatment with 5% cold rolling followed by annealing at 1000℃ for 1 h,the fraction of special boundaries(SBs) increases from 38.4% in conventional alloy to 77.2% and the fraction of special triple junctions increases from 10% to 74%.During 800℃ aging treatment,quite amount of cellular η phases adjacent to random grain boundary(RGB) will be found in conventional alloy,and only a few small η phases have been observed in GBE treatment alloy subjected to the same aging treatment for long time.The reason for GBE in inhibiting precipitation of η phase can be attributed to not only introducing high fraction of SBs but also breaking the connectivity of RGB networks.As nucleation and growth of η phases on SBs are difficult due to their lower Ti concentration and diffusion rate,and the disruption of RGB networks reduces supply of Ti atoms to the η phases significantly,which impedes their growth at RGB.

Freezing of Water in a Slab with Boundary Conditions of the Third Kind

Predictions for freezing heat transfer in a slab with convective boundary conditions at the cold surfaceare obtained from heat balance integral approximations, which consider conduction as the only modeof heat transfer in both the solid and liquid and consider durations of precooling and freezing in theheat transfer process. The thermal penetration dimensionless parameter or is presented to distinguishtwO cases of freezing, and analytical results for α≥ 1 are given in this paper. An experimental investigation on freezing of water is reported for comparison with the one-dimensional conduction model toshow that experimental modeling for freezing heat transfer with convective boundary conditions usingPeltter devices is feasible. The comparison also demonstrated that the freezing rate in this case wasdecreased by natural convection in the liquid just as freezing with boundary conditions of the first kindand phase change approximately proceeds linearly with time rather than with square root of time atthe initiation of freezing.

On δ-reducible Heegaard Splittings

In this paper, we shall prove that any Heegaard splitting of a δ-reducible 3-manifold M, say M = W U V, can be obtained by doing connected sums, boundary connected sums and self-boundary connected sums from Heegaard splittings of n manifolds M1,..., Mn, where Mi is either a solid torus or an irreducible, δ-irreducible manifold.

Saliency Detection via Manifold Ranking Based on Robust Foreground

The graph-based manifold ranking saliency detection only relies on the boundary background to extract foreground seeds,resulting in a poor saliency detection result,so a method that obtains robust foreground for manifold ranking is proposed in this paper.First,boundary connectivity is used to select the boundary background for manifold ranking to get a preliminary saliency map,and a foreground region is acquired by a binary segmentation of the map.Second,the feature points of the original image and the filtered image are obtained by using color boosting Harris corners to generate two different convex hulls.Calculating the intersection of these two convex hulls,a final convex hull is found.Finally,the foreground region and the final convex hull are combined to extract robust foreground seeds for manifold ranking and getting final saliency map.Experimental results on two public image datasets show that the proposed method gains improved performance compared with some other classic methods in three evaluation indicators:precision-recall curve,F-measure and mean absolute error.

Influence of the connecting condition on the dynamic buckling of longitudinal impact for an elastic rod

The stress wave propagation law and dynamic buckling critical velocity are formulated and solved by considering a general axial connecting boundary for a slender elastic straight rod impacted by a rigid body. The influence of connecting stiffness on the critical velocity is investigated with varied impactor mass and buckling time. The influences of rod length and rod mass on the critical velocity are also discussed. It is found that greater connecting stiffness leads to larger stress amplitude, and further results in lower critical velocity. It is particularly noteworthy that when the connecting stiffness is less than a certain value, dynamic buckling only occurs before stress wave reflects off the connecting end. It is also shown that longer rod with larger slenderness ratio is easier to buckle, and the critical velocity for a larger-mass rod is higher than that for a lighter rod with the same geometry.