Improved Tribocorrosion Resistance by Addition of Sn to CrFeCoNi High Entropy Alloy

Among the high entropy or complex concentrated alloys (HEAs/CCAs), one type of system is commonly based on CoCrFeNi, which as an equiatomic quaternary alloy that forms a single phase FCC structure. In this work, the effect of Sn in an equiatomic quinary system with CoCrFeNi is shown to lead to a great improvement in hardness and resistance to tribocorrosion. The addition causes a phase transition from a single FCC phase in CoCrFeNi to dual phase in CoCrFeNiSn with an Ni-Sn intermetallic phase, and a CoCrFeNi FCC phase. The presence of both the hard intermetallic and this ductile phase helps to resist crack propagation, and consequent material removal during wear. In addition, the high polarization resistance of the passive film formed at the surface and the high corrosion potential of the Ni-Sn phase contribute to preventing chloride corrosion attack during corrosion testing. This film is tenacious enough for the effect to persist under tribocorrosion conditions.

Study on Fracture Energy of Cement Stabilized Aggregate

A series of parametric tests have been conducted to investigate the effect of curing period and cement content of the specimen on fracture energy of cement stabilized aggregate. By means of three-point bending method, the fracture energy of cement stabilized aggregate was measured. Four specimen curing periods (14 d, 28 d, 60 d and 90 d) and four different cement contents (4%, 5%, 6% and 7%) were used. The results indicate that the fracture energy of cement stabilized aggregate is increasing with the increase of specimen curing period. Besides, with the increase of cement content, there is a tendency to decrease in the fracture energy of cement stabilized aggregate. The ability of cement stabilized aggregate to resist crack propagation becomes weaker and weaker with the increase of cement content.

The Influence of Crystallographic Orientation of the Crack Plane and Crack Front on the Fracture of Tungsten Single Crystals

For fracture studies on oriented W monocrystalline specimens it is necessary to produce very sharp, stopped precracks, which presents difficulties in the case of W. The experimental procedure and technique to produce precracks is described. The fracture experiments gave strong indications for a preference of the {100} plane as cleavage plane. It was found that the {110} planes successfully resist crack propagation, although they are the planes with the lowest surface energy. The appearance of the {121} plane as a cleavage plane in our experiments makes further studies with oriented W monocrystalline samples necessary.