Effect ofαphase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.

Tribological properties improvement of conventionally-cast Al−8.5Fe−1.3V−1.7Si alloy by multi-pass friction stir processing

The effect of multi-pass friction stir processing(FSP)on the tribological properties of conventionally-cast Al−8.5Fe−1.3V−1.7Si(FVS0812)alloy was investigated.The pin-on-disk dry sliding wear tests were conducted at room temperature under the applied pressures of 0.25,0.50,and 0.75 MPa.The results showed that FSP substantially refined and improved the distribution of coarse¸-Al_(13)Fe4 platelets andα-Al_(12)(Fe,V)_(3)Si intermetallics in the microstructure of alloys and eliminated the intermetallic-related defects.Consequently,the mechanical properties of the alloys,especially their ductility,were improved,which enhanced the stability of the protective tribolayer formed on their worn surfaces.According to the wear test results,the FSPed samples showed improved tribological properties especially at the higher applied pressures.For instance,at the applied pressure of 0.75 MPa,the wear rate and average friction coefficient of four-pass FSPed sample were lower than those of the base as-cast sample by 97%and 52%,respectively.SEM examination of the worn surfaces and wear debris also demonstrated that the wear mechanism changed from severe delamination/abrasion and microcracking of the tribolayer in the as-cast samples to mild delamination/abrasion and minor plastic wear in the FSPed samples.

Influence of Neodymium on Amorphizability of RS Al-Fe-V-Si-Nd Alloys:An Investigation Using Time Dependent Nucleation Theory

Time dependent nucleation theory was applied to calculate the incubation time required for α Al nucleation in rapid solidified (RS) Al Fe V Si Nd alloys. The nucleation rates were calculated as a function of temperature, and the critical cooling rates required for the formation of amorphous α Al at different neodymium concentrations were calculated too. The addition of neodymium increases the amorphizablity of α Al by increasing the incubation time and decreasing the nucleation rate and the critical cooling rate. The calculations are fitted to experimental results when liquidus temperatures are estimated from an approximation, which treats Al Fe V Si Nd as quasi binary Al Fe system.

Selective Laser Melting of an Al–Fe–V–Si Alloy:Microstructural Evolution and Thermal Stability

Selective laser melting was used to produce an aluminum alloy Al-8.5Fe-1.3V-1.7Si（wt%）. The effects of heat treatment on microstructure evolution and phase stability during long-term thermal exposure of the deposits were investigated. Results show that the microquasi-crystalline phase, Al12（Fe,V）3Si and AlmF e metastable phases coexisted with α-Al in the as-produced alloy. Annealing at 400 ℃ resulted in decomposition of microquasi-crystalline phase and supersaturated α-Al into Al12（Fe, V）3Si phase in the fusion zone, accompanied by the decrease in alloy hardness. The activation energy of this decomposition process was 115 k J/mol. A more homogenous microstructure was obtained after annealing at 400 °C for 60 min,which was resistant to coarsening exposed at 425 °C up to 500 h. The Al12（Fe,V）3Si and AlmF e phases were coarsened at 475 and 525℃ with increasing the exposure time. Coarsening of Al12（Fe,V）3Si phase was attributed to a combination of volume diffusion and grain boundary diffusion mechanism of Fe. Heat treatment at 600℃ resulted in accelerated microstructure coarsening and formation of large-sized equilibrium phases, which signi？cantly degraded the room temperature microhardness.

Tribological Properties of Nanostructured Al/Al_(12)(Fe,V)_3Si Alloys

Tribological behavior of nanostructured pure Al and Al–Al12（Fe,V）3Si alloys containing 27（FVS0812） and 37（FVS1212） vol% of Al12（Fe,V）3Si precipitates was investigated. All samples were prepared using mechanical alloying followed by hot pressing. Wear tests were performed at room temperature using a pin-on-disk machine. Results showed that the presence of Al12（Fe,V）3Si precipitates increases the wear resistance of nanostructured Al, and the wear resistance increases with increasing the Al12（Fe,V）3Si content. Scanning electron microscopy images of worn surfaces and wear debris demonstrated that abrasion and adhesion are the governing wear mechanisms for the nanostructured FVS0812 alloy at 2 and 5 N normal loads, whereas for the nanostructured FVS1212 alloy, the dominant wear mechanism is abrasion at these loads. A mechanically mixed layer（MML） containing Fe and O was formed on the worn surfaces of FVS0812 and FVS1212 samples at 10 N normal load. Formation and delamination of MML controls the wear behavior of these samples at the normal load of 10 N. It is also found that the presence of Al12（Fe,V）3Si precipitates decreases the friction coefficient of nanostructured Al.

Correlation Between Magnetic Properties and Allotropic Phase Transition of Fe–Co–V Alloy

In this study, the allotropic phase transition and its effect on the magnetic behavior of Fe Co–7 wt%V alloy were investigated. It was found that c phase is observed in the microstructure in the as-cast condition, and it diminishes after severe cold rolling（90% reduction）. After annealing at temperatures higher than 500 up to 750 ℃, the c phase is observed in the structure, again. But, this phase is disappeared by annealing at temperatures above 750 ℃ due to the formation of vanadium-rich precipitates. Thermocalc software was used in order to elucidate the influence of vanadium percent on the stability of c phase in Fe–Co alloys. Also, magnetic studies showed that the saturation induction is reduced by annealing at temperatures from 500 up to 750 ℃, which is related to the formation of residual non-magnetic γ phase.