Yaping Bai

Tribological properties of in situ Fe3Al-20 wt% Al2O3 composites

The tribological properties of Fe3Al-20 wt% Al2O3 composites, prepared by means of mechanical alloying and plasma-activated sintering, were investigated under air atmosphere against GCr15 bearing steels from room temperature to 500 °C. It was found that the friction coefficient of the composites (at 200 °C/350 °C) decreased with increasing temperature and the value was lower than that of Fe3Al alloys at the same temperature, and the friction coefficient increased again at 500 °C. Moreover, the wear rates of all the pins and discs were low at the medium/high temperatures. The dominant wear mechanism of the composites is microplowing and a little oxidation wear at room temperature. However, at elevated temperatures, oxidation wear and a little microplowing are found to be the main wear mechanism. There is also spalling induced by microfracture at 500 °C. The in situ Fe3Al-20 wt% Al2O3 composites have excellent wear resistance at a wide temperature range.

Effect of Al2O3 nanoparticle reinforcement on the mechanical and high-temperature tribological behavior of Al-7075 alloy:

In this paper, Al2O3/7075 composites were prepared by mechanical alloying with subsequent hot-pressing sintering, and the effect of Al2O3 nanoparticle on the mechanical and tribological behavior of 7075 was studied. The mechanical property results showed that the hardness and compressive strength of Al2O3/7075 composites first increased and then decreased with Al2O3 amount increasing, and 5 wt.% Al2O3 addition made the material exhibit excellent comprehensive mechanical properties. The tribological properties also indicated that 5 wt.% Al2O3 nanoparticle significantly improved the high-temperature wear resistance of 7075 alloys. Thus, all the mechanical and tribological results confirmed that the addition of Al2O3 nanoparticle was a better strengthening way for 7075 alloys at high temperatures.

Effect of MoS2 on the tribological properties of in situ Fe3Al-20 wt% Al2O3-4 wt% Cr composites

Fe3Al-20 wt% Al2O3-4 wt% Cr composites containing 0, 5 and 8 wt% MoS2 were subjected to mechanical alloying-inducing self-propagating high temperature synthesis with subsequent hot-pressing sintering. Microstructures of the composites were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectrum analysis. Then the relative density, room temperature hardness and dry sliding wear behavior of the sintered composites at 25 °C, 500 °C and 800 °C were tested and analyzed. The results showed that composites with different amounts of added MoS2 had good microstructure with high relative density and high hardness. The MoS2 decomposes during sintering with the formation of Fe3Mo3C and Cr2S3. Cr2S3 formed from the decomposition process may form a lubricating film that can decrease the friction coefficient. At 800 °C, Fe3Al-20 wt% Al2O3-4 wt% Cr with 8 wt% added MoS2 exhibited a friction coefficient that was nearly 50% lower than that for the sample with no MoS2 addition. Addition of 8 wt% MoS2 transformed the wear mechanism from adhesive wear to microploughing.

STATIC CORROSION BEHAVIOR OF IN-SITU NANOCRYSTALLINE Al2O3/Fe(Al) COMPOSITES

In this work, the static corrosion behaviors of Fe(Al), and 20 wt.% Al2O3/Fe(Al) composites with and without 4 wt.% Cr produced by mechanical alloying (MA) and plasma activated sintering (PAS) were investigated. The results showed that the main corrosion failure mode was pitting, and Fe(Al) had higher static corrosion resistance than those of Al2O3/Fe(Al) composites. The second phase Al2O3 addition resulted in an increase in phase interface and a large difference of the electron density between the Fe(Al) matrix and Al2O3 reinforcement. All these made the phase interface become the corrosion weaknesses. With 4 wt.% Cr addition, the static corrosion weight loss rate reduced by about 20% because Cr element could improve the stability of Al2O3 passivation film on the composite surface.

Effects of Solidification Cooling Rate on the Microstructure and Mechanical Properties of a Cast Al-Si-Cu-Mg-Ni Piston Alloy

The effects of cooling rate 0.15, 1.5, 15, 150, and 1.5 × 105 °C/s on the microstructures and mechanical properties of Al-13Si-4Cu-1Mg-2Ni cast piston alloy were investigated. The results show that with an increase of solidification cooling rate, the secondary dendrite arm spacing (SDAS) of this model alloy can be calculated using the formula D = 47.126v − 1/3. The phases formed during the solidification with lower cooling rates primarily consist of eutectic silicon, M-Mg2Si phase, γ-Al7Cu4Ni phase, δ-Al3CuNi phase, ε-Al3Ni phase, and Q-Al5Cu2Mg8Si6 phase. With the increase in the solidification cooling rate from 0.15 to 15 °C/s, the hardness increased from 80.9 to 125.7 HB, the room temperature tensile strength enhanced from 189.3 to 282.5 MPa, and the elongation at break increased from 1.6% to 2.8%. The ε -Al3Ni phase disappears in the alloy and the Q phase emerges. The δ phase and the γ phase change from large-sized meshes and clusters to smaller meshes and Chinese script patterns. Further increase in the cooling rate leads to the micro hardness increasing gradually from 131.2 to 195.6 HV and the alloy solidifying into a uniform structure and forming nanocrystals.

Tribological behavior of in-situ (Cr, Mo)/Fe3Al-20 wt.%Al2O3 composites at elevated temperatures

Dry-sliding tribological performance of in-situ Fe3Al-20 wt.%Al2O3, (4 wt.%Cr)/Fe3Al-20 wt.%Al2O3, and (4 wt.%Cr, 5 wt.%Mo)/Fe3Al-20 wt.%Al2O3 composites, produced by mechanically induced self-propagating mechanism and plasma-activated sintering, was investigated against Inconel718 from 25℃ to 800℃ under air/argon atmosphere. It can be found that (4 wt.%Cr, 5 wt.%Mo)/Fe3Al-20 wt.%Al2O3 composite exhibits more excellent comprehensive tribological properties with the friction coefficient decrease nearly 67% compared to Fe3Al-20 wt.%Al2O3 composite above 350℃ due to the balance between strength and lubricity. At 800℃, the dominant wear mechanism is oxidation wear under air condition, whereas under argon atmosphere, the actual wear mechanism is mainly transferred to microploughing.