Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

An experimental 2618（Al-Cu-Mg-Fe-Ni） alloy added with trace Sc and Zr was prepared by ingot metallurgy （IM） method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al3（Sc,Zr） phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al3（Sc,Zr） particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S’ phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.

Effect of Hydrogen on Cryogenic Mechanical Properties of Cr-Ni-Mn-N Austenitic Steels

The method of high-pressure hydrogen charging was used to investigate the internal hydrogeneffects on cryogenic mechanical properties of two Cr-Ni-Mn-N austenitic steels, 22-13-5 and21-6-9. Specimens saturated with hydrogen up to 65×10-6～68×10-6 were tested in air attemperatures ranging from 77 to 293 K. Hydrogen caused the increase in cryogenic strength,both yield strength and ultimate tensile strength. Hydrogen decreased cryogenic ductility, andthe maximum hydrogen embrittlement (HE) tendency was found at a certain low temperature.Cr-Ni-Mn-N auStenitic Steels showed the featuref δL > ΨL at low temperatures, here, δL and ΨLare the hydrogen induced loss rates of elongation and reduction of area, respectively. Hydrogenhad less effect on cryogenic Charpy impact toughness and notched tensile strength, however,hydrogen decreased cryogenic fracture toughness of the steels. At temperature below Md, thefracture toughness was obviously decreased due to the formation of strain-induced martensites,whether hydrogen was charged or not.

Annealing Effect on Mechanical Properties of Ti_(51)Ni_(13)Pd_(36)High Temperature Memory Alloy

The high temperature shape memory alloy Ti51Ni13Pd36 was subjected to a cold working and annealing treatment to improve its mechanical properties and the shape memory effect. It was found that recovery of the cold worked alloys started at near 673 K and the recrystallization temperature was at about 748 K. The grain size decreased with the increase of annealing temperature below 923 K and then increased when above 923 K. The smallest average grain size of about 3.5μm, which is approximately 10 times smaller than the hot rolled one, permitted the best combination of the mechanical properties in the alloy annealed at 923 K for 1h. The cold rolling raised the peak temperature of reverse transformation. This temperature dropped very sharply when the specimen was annealed at temperatures higher than 673 K.

Effect of Mineral Oil on the Mechanical Properties and Fractographs of Fe_3(Al,Cr,Zr) Intermetallic Alloy

The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil is comparable with the results obtained in oxygen and is in sensitive to strain rate. The fracture mode of the Fe3(Al,Cr,Zr) alloy treated at 700℃/1.5 h and tested in oil, is cleavage and with dimples in some areas.

Effects of A1 Additions on Microstructure and Mechanical Properties of MoSi_2

The effects of Al additions on the microstructure and mechanical properties of MoSi2 have been studied. With the A1 additions from 2.5 wt pct to 5 wt pct, the siliceous grain boundary phase in hot pressed samples was eliminated because of the formation of Al2O3 particles. It was shown that Al and SiO2 reacted at 860℃. During the reaction, A1 atoms were mainly transferred to Al2O3 particles, and to some extent, diffused into MoSi2 grains. Both the toughness and strength of Al containing composites exceeded those of pure MoSi2 material. Bending strength and fracture toughness reach the highest value of 350 MPa, 4.05 MPa.m1/2, respectively, at ambient temperature when Al addition was of 3.5 wt pct.

Hydrogen Effects on the Mechanical Properties of Ti-24Al-11Nb-3V-1Mo Alloy

The effects of hydrogen on the mechanical properties at room temperature of a Ti3Al based alloy Ti-24Al-11Nb-3V-1Mo have been investigated. The results show a parabolic rate relationship between the average hydrogen concentration of the alloy at constant temperature and charging time. The mechanical properties (ultimate bending strength and deflection) decrease with increasing hydrogen content in the alloy. The fractographic feature indicates that the decrease of the mechanical properties is due to the crack nucleation and propagation at the hydride

Effects of Mg on Mechanical Properties of 35CrNi3MoV Steel

The effects of Mg on the mechanical properties of 35CrNi3MoV steel has been studied in this paper. The results show that Mg has less effect on the tensile properties and hardness of the steel at room temperature, but a right amount of Mg improves impact and fracture toughness and decreases the fracture-transition temperature considerably due to inclusions modification, as well as prolongs the notch stress rupture life dramatically through strengthening grain boundary and modifying boundary carbides. There is an optimum Mg content, which is about 0.0030% in the experimental 35CrNi3MoV