The tribological behavior of Mg97Zn1Y2 alloy was investigated using a pin-on-disk wear machine at wear temperatures of 50-200 °C. Morphologies and chemical compositions of worn surfaces were analyzed using scanning electron microscope and energy-dispersive x-ray spectrometer. The microstructural evolution and hardness change in subsurfaces were examined by optical microscopy and hardness tester. The results showed that the wear temperature had significant influence on the coefficient of friction and wear rate. At wear temperatures of 50-200 °C, with increasing applied load, the coefficient of friction went down rapidly then turned to decrease slowly in the mild wear regime, and continuously decreased modestly until the largest applied load in the severe wear regime. Increasing wear temperature from 50 to 200 °C decreased the mild to severe wear transition load linearly from 120 to 60 N. In the mild wear regime, the main wear mechanisms were identified as abrasion + oxidation and delamination + surface oxidation at 50-150 °C, and delamination at 200 °C, while in the severe wear regime, the main wear mechanisms were identified as severe plastic deformation + spallation of oxide layer and surface melting at 50-150 °C, and severe plastic deformation and surface melting at 200 °C. The microstructural transformation from the deformed to the dynamically recrystallized (DRX), and hardness change from the strain hardening to softening were found in the subsurfaces before and after mild to severe transition. The DRX softening mechanism was determined for mild to severe wear transition at 50-200 °C. A wear transition map was constructed for Mg97Zn1Y2 alloy on applied load versus wear temperature.

This paper describes a novel method for predicting the mild to severe wear transition loads for AZ31 and AZ61 alloys at various sliding velocities. Morphologies and hardness of worn surfaces and microstructures in subsurfaces of AZ31 alloy were analyzed. A criterion of mild to severe wear transition is proposed, i.e., the mild to severe wear transition is controlled by a critical surface dynamic recrystallization (DRX) temperature. DRX temperatures in surface layers at transition loads are determined using recrystallization kinetics. Correlation between DRX temperature and transition load is established by introducing a constant cDRX that is associated with testing equipment and material properties of pin and disk in the critical DRX state. The transition loads are well predicted in a sliding velocity range of 0.5-4.0 m/s for AZ31 alloy, and 0.8-2.0 m/s for AZ61 alloy.

•Subsurface microstructural evolution influences the wear rate of AZ31 alloy.•Transition from mild to severe wear was controlled by DRX in surface layer.•Mild to severe wear transition loads were evaluated using DRX kinetics.•We construct the surface microstructural evolution map of AZ31 alloy.Dry sliding tests were performed on as-cast AZ31 magnesium alloy using a pin-on-disc configuration. Coefficients of friction and wear rates were measured within a load range of 5–360 N and a sliding velocity range of 0.1–4.0 m/s. Morphologies, compositions and hardness of worn surfaces were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and hardness tester. Microstructural evolution, strain hardening and dynamic crystallization (DRX) generated in subsurfaces of AZ31 alloy during sliding were found to correlate with the tribological properties obtained. The subsurface microstructures beneath the contact surface were subjected to large plastic strains, and experienced strain hardening, DRX and melting as a result. The roles of surface hardening and thermal softening on the mild to severe wear transition were investigated in detail. It was shown that the transition occurred when the surface layer softened with DRX. Surface oxidation and strain hardening played an important role in maintaining the mild wear, and thermal softening originating from DRX in subsurface and surface melting were responsible for the severe wear. A transition load model, which can be used predict the critical load for transition from mild to severe wear, has been developed using the method of DRX kinetics. A map has been constructed for presenting microstructural evolution and hardness change in surface layer based on the calculated mild to severe wear transition loads and critical loads for surface melting.

The corrosion behaviours of non-boronized and boronized AISI 8620 steels in both oil field water and H2S-saturated oil field water have been investigated by means of immersion test, electrochemical method, X-ray diffraction and scanning electron microscopy. The experimental results show that boronized steel has better corrosion resistance to as-received oil field water and H2S-saturated oil field water than the non-boronized steel. Both non-boronized and boronized steels have reacted with H2S and form corrosion film of FeS, which could not retard the corrosion process due to pores and cracks in the FeS film, and large scale of pitting corrosion is found on non-boronized AISI 8620 steel surface. The immersion corrosion of non-boronized AISI8620 in both corrosion solutions can be divided into two stages: the rapid corrosion stage with high slope and the gradual corrosion stage with low slope, corresponding to uniform corrosion and corrosive product scaling off the surface, respectively. The better corrosion resistance shown by boronized AISI 8620 steel is ascribed to lower corrosion current as compared with the non-boronized AISI8620 steel.

The effect of boronizing from solid phase on the tensile mechanical properties and corrosion and wear resistances of steel AISI 8620 is studied. Boronizing is shown to have a positive effect on the corrosion and wear performance of oilfield sucker rods.

Mg-11Y-2.5Zn alloy was surface-melted using a 6.0 kW continuous wave CO2 laser as a heat-generating source. X-ray diffractometer, laser optical microscopy, and Vickers hardness indentation were used to characterize the microstructure and hardness of the Mg-11Y-2.5Zn alloy. The results show that the microstructure in the laser-melted zone can be greatly refined and hardness is slightly improved. Dry sliding tests were performed on the as cast and laser surface-melted Mg-11Y-2.5Zn alloys using a pin-on-disk configuration. Coefficients of friction and wear rates were measured within a load range of 20-320 N at a sliding velocity of 0.785 m/s. Laser surface-melted Mg-11Y-2.5Zn alloy exhibited good wear resistance when compared with the as cast one under given applied load conditions, which has been explained by refining of the microstructure in the melted zone. Morphologies of worn surface on the as cast and laser surface-melted Mg-11Y-2.5Zn alloys were examined using scanning electron microscopy. Four wear mechanisms, namely abrasion, delamination, thermal softening, and melting, have operated.

Mg97Zn1Y2 magnesium alloy was hot-rolled at different temperatures from 390 to 480 °C; the effect of rolling temperature on microstructure evolution and mechanical properties of Mg97Zn1Y2 magnesium alloy was investigated using x-ray diffraction (XRD), laser optical microscopy (LOP), transmission electron microscopy (TEM), and tensile test. The results showed that in the multipass process, the rolling temperature had significant effect on the microstructures and tensile properties for the hot-rolled Mg97Zn1Y alloy. As the rolling temperature was increased, the original strengthening phase-Mg12YZn in as-cast Mg97Zn1Y2 alloy experienced an evolution from dissolution to precipitation, i.e. from chain-shaped Mg12YZn phase together with a little lamellar structure at 420 °C to a maximum volume fraction of lamellar structure at 450 °C, and finally to a reduced volume fraction of lamellar structure at 480 °C. For Mg97Zn1Y2 alloy hot-rolled in the temperature range of 390-450 °C, the tensile strength was at a high level with yielded strength of about 300 MPa and ultimate strength of about 320 MPa. The highest yielded strength was 317 MPa after hot-rolling at 450 °C; the elongation was the highest up to 5.5% after hot-rolling at 420 °C.

The microstructures and tensile properties of boronized N80 steel pipes by pack boriding under four different cooling conditions were investigated. The boride layer was composed of FeB and Fe2B phases with a hardness range of 1200-1600 HV. Fan cooling and fan cooling with a graphite bar in the center of the boriding agent were employed to improve the tensile properties. As cooling velocity was increased, the thickness of boride layer and grain size of the steel substrate were consequently reduced, whereas the pearlite volume in steel substrate was increased, resulting in improvement of tensile properties. Boronized N80 steel pipe which was fan cooled with a graphite bar inside possessed the highest ultimate tensile strength and yield strength, in accordance with the mechanical properties required by API SPEC 5L. Fracture surface analysis revealed that the boronized N80 steel showed ductile fracture at room temperature.

Dry sliding tests were performed on as-cast magnesium alloys Mg97Zn1Y2 and AZ91 using a pin-on-disc configuration. Coefficients of friction and wear rates were measured within a load range of 20–380 and 20–240 N at a sliding velocity of 0.785 m/s. X-ray differactometer, scanning electron microscopy, tensile testing machine were used to characterize the microstructures and mechanical properties of Mg97Zn1Y2 alloy and AZ91 alloy. Worn surface morphologies of Mg97Zn1Y2 and AZ91 were examined using scanning electron microscopy. Five wear mechanisms, namely abrasion, oxidation, delamination and thermal softening and melting, have been observed. Mg97Zn1Y2 exhibited good wear resistance compared with AZ91 for applied loads in excess of 80 N, which have been explained in terms of thermal stability of intermetallic phase and elevated temperature mechanical properties of the two materials tested, using surface temperature analysis.

In the present work, Al–Pb alloy was irradiated by high current pulsed electron beam. X-ray diffractometer, electronic probe microanalysis, scanning electron microscopy and Knoop hardness indentation were used to characterize the microstructure and mechanical property of Al–Pb alloy. The results show that the microstructure and mechanical property can be greatly improved. The tribological properties of high current pulsed electron beam irradiated Al–Pb alloy were investigated under dry sliding conditions using a pin-on-disc type wear testing machine. The overlapped zone beneath the melted zone exhibits good resistance to wear. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al–Pb alloy are due to a lubricious tribolayer covering almost the entire worn surface. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.

The tribological properties of Al–Si–Pb alloys irradiated by high current electron beam (HCPEB) were investigated under dry sliding conditions using a pin-on-disc type wear testing machine. The HCPEB parameters used to treat the samples are: electron energy: 21–25 keV; energy density: 1.5–2.5 J/cm2; pulse duration: 1.5 μs; number of pulses: 15. The results show that the microstructure and mechanical properties can be greatly improved. These factors contribute to great increase in wear resistance of HCPEB irradiated Al–Si–Pb alloys at 2.0 J/cm2 and 2.5 J/cm2. Optical observation and X-ray photoelectron spectroscopy (XPS) analysis reveal that the low wear rate and lowest level in coefficient of friction at high load levels for Al–Si–Pb alloys HCPEB irradiated with more than 1.5 J/cm2 are due to a film of lubricant covering almost the entire worn surface. This film is a mixture of different constituents containing Al, Fe, Si, O and Pb, in which Pb exists in the form of Pb4SiO6. With the applied load increased, the dominant wear modes exhibit successively the oxidative wear, film spalling, and adhesive wear.