Search

In the present study, the unique three-dimensional graphene coated nickel (Ni/C) foam reinforced silicon carbide (Ni/C@SiC) composites were first obtained via the precursor impregnation and pyrolysis (PIP) processes. The microstructure images indicated that the SiC fillers were successfully prepared in the skeleton pores of the Ni/C foam. The influence of the PIP cycles on the microwave absorption performances was researched, and the results indicated that after the primary PIP process, Ni/C@SiC–I possessed the optimal microwave absorbing performance with a minimum reflection loss(RL) of −25.87 dB at 5.28 GHz and 5.00 mm. Besides, the RL values could be below −10.00 dB from 5.88 GHz to 7.74 GHz when the corresponding matching thickness was 3.85 mm. However, the microwave absorption properties of Ni/C@SiC-II and Ni/C@SiC-III were tremendously degraded as the PIP times increased. At last, the electromagnetic parameter, dielectric loss, attenuation constant as well as impedance matching coefficient were further investigated to analyze the absorbing mechanism, which opened a new path for the certain scientific evaluation of the absorbing materials and had extremely important to the defence technology.

Level-specific lumbar bone mineral density (BMD) evaluation of a single vertebral body can provide useful surgical planning and osteoporosis management information. Previous comparative studies have primarily focused on detecting spinal osteoporosis but not at specific levels.To compare the detection rate of lumbar osteoporosis between quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA); to explore and analyze the distribution models of QCT-derived BMD and DXA T-score at the specific levels; and to evaluate the diagnostic accuracy of level-specific BMD thresholds for the prediction of osteoporotic vertebral compression fracture (OVCF) in postmenopausal women.A comparative analysis of prospectively collected data comparing QCT-derived BMD with DXA T-score.A total of 296 postmenopausal women who were referred to the spine service of a single academic institution were enrolled.QCT-derived BMD and DXA T-score at specific levels, with or without osteoporotic vertebral compression fracture.Postmenopausal women who underwent QCT and DXA within a week of admission from May 2019 to June 2022 were enrolled. The diagnostic criteria for osteoporosis recommended by the World Health Organization and the American College of Radiology were used for lumbar osteoporotic diagnosis. To evaluate differences in lumbar BMD measurements at specific levels, a threshold of T score=-2.5 and QCT-derived BMD = 80 mg/cmOf the 296 patients, QCT diagnosed 61.1% as osteoporosis, 30.4% as osteopenia and 8.4% as normal. For those screened with DXA, 54.1% of the patients had osteoporosis, 29.4% had osteopenia and 16.6% had normal BMD. Diagnoses were concordant for 194 (65.5%) patients. Of the other 102 discordant patients, 5 (1.7%) were major and 97 (32.8%) were minor. Significant correlations in level-specific BMD between DXA and QCT were observed (p.001), with Pearson's correlation coefficients ranging from 0.662 to 0.728. The correlation strength was in the order of L1L2L3L4. The low BMD detection rate for QCT was significantly higher than that for DXA at the L3 and L4 levels (65% vs. 47.9% and 68.1% vs 43.7, respectively, p.001). Patients with OVCF showed significantly lower QCT-derived BMD (47.2 mg/cmQCT provided a more accurate evaluation of lumbar osteoporosis than DXA. The QCT-derived BMD measurements at a specific lumbar level have a high diagnostic performance for OVCF.

A porcine model.The study aims to design a novel pedicle navigator based on micro-inertial navigation system (MINS) and bioelectrical impedance analysis (BIA) to assist place pedicle screw placement and validate the utility of the system in enhancing pedicle screw placement.The incidence of pedicle screw malpositioning in complicated spinal surgery is still high.Procedures such as computed tomography image-guided navigation, and robot-assisted surgery have been used to improve the precision of pedicle screw placement, but it remains an unmet clinical need.The miniaturized integrated framework containing MINS was mounted inside the hollow handle of the pedicle finder. The inner core was complemented by a high-intensity electrode for measuring bioelectric impedance. Twelve healthy male Wuzhishan minipigs of similar age and weight were used in this experiment and randomized to the MINS-BIA or freehand (FH) group. Pedicle screw placement was determined according to the modified Gertzbein-Robbins grading system on computed tomography images. An impedance detected by probe equal to the baseline value for soft tissue was defined as cortical bone perforation.A total of 216 screws were placed in 12 minipigs. There were 15 pedicle breaches in the navigator group and 31 in the FH group; the detection rates of these breaches were 14 of 15 (93.3%) and 25 of 31 (80.6%), respectively, with a statistically significant difference between groups. The mean offsets between the planned and postoperatively measured tilt angles of the screw trajectory were 4.5° ± 5.5° in the axial plane and 4.8° ± 3.3° in the sagittal plane with the navigator system and 7.0° ± 5.1° and 7.7° ± 4.7°, respectively, with the FH technique; the differences were statistically significant.A novel and portable navigator based on MINS and BIA could be beneficial for improving or maintaining accuracy while reducing overall radiation exposure.

ZrO2/yttria-stabilized zirconia (YSZ) doping Al2O3 ceramic coating was fabricated via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and the chemical and phase compositions of the doped coating were characterized, the mechanical properties and the high temperature oxidation resistance were evaluated, and the doping mechanism was also discussed in detail. The results showed that, doped Zr4+ and Y3+ ions could effectively reduce the working voltage during CPED process and increase the content of metastable γ-Al2O3 in the coating. Accordingly, the doped ZrO2/YSZ significantly refined the grain size of Al2O3, as well as remarkably improved the high temperature oxidation resistance, the micro-structural compactness and hardness of the Al2O3 CPED coating. This study displayed here constructed an efficiently method for the fabrication of multifunctional coating on the surface of TiAl alloy.

CeO2 doped Al2O3 composite ceramic coatings were fabricated on TiAl alloys via cathodic plasma electrolytic deposition technique in 0.3 mol/L Al(NO3)3 ethanol electrolytes containing different concentrations of Ce(NO3)4. The effects of CeO2 doping contents on microstructures, elemental compositions, mechanical properties, high temperature oxidation resistance at 850 °C, and wear resistance against GCr15 balls at 200 °C of the coatings were investigated. The results indicated that the contents of CeO2 in composite coatings increased with increasing concentration of Ce(NO3)4, and composite coatings were composed of α–Al2O3 mainly, γ–Al2O3, and a little CeO2. The doping of CeO2 helped to improve the phase inversion from γ–Al2O3 to α–Al2O3. The crystallization and wear resistance of composite coatings increased due to the doping of CeO2. In the electrolyte containing 0.015 mol/L Ce(NO3)4, the coating was the most uniform and compact, and of the best high temperature oxidation resistance and mechanical properties.

The knowledge of process parameters–weld integrity-aging treatments–tensile property relationship is of great concern for linear friction welded (LFWed) Ti2AlNb-based alloy and requires a systematic characterization. Thus, the Ti2AlNb-based alloy was LFWed under various process parameters and then subjected to different aging treatments. Twelve welding conditions were used to evaluate the weld integrity, showing that impurities and cracks at weld interface can be eliminated under strong welding parameters and the feed rate has the greatest influence on the weld integrity among all process parameters. Relationships among aging temperatures, microstructure evolution, and mechanical properties were investigated. After aging treatment, acicular O phase has precipitated in B2 grains both in the weld zone and thermo-mechanical affected zone (TMAZ). The size of precipitated O phase increases along with the increase of temperature, and the α2 + O mixtures have finally decomposed into the aggregated acicular O phase. The microhardness and tensile strength of the joints have been enhanced due to the precipitation hardening of O phase and refined grain strengthening after aging treatments.

In order to increase the surface hardness and wear-resistance property of sled track slippers, a Ni80Al20-MoS2 composite coating was fabricated on the surface of a stainless steel 0Cr18Ni9Ti sled track slipper via atmospheric spray and hot dipping. The microstructure, composition and surface hardness of coatings under different spraying powers were characterized and measured. The wear-resistant properties of the slipper substrate and the coating were also checked. The results showed that the higher the spraying power was, the greater the smoothness, density and hardness was of the Ni80Al20 coating, while the thickness initially increased and then decreased. When the spraying power was 18 kW, the thickness was 342.5 &mu, m, the surface hardness was 304.1 Hv0.2, and the coating was composed of Ni, Al, Ni3Al, NiAl and a little Al2O3. The friction coefficient of the slipper substrate against GCr15 balls at room temperature in air was 0.7, while the coated substrate with MoS2 lubrication film was 0.3 and the volume wear rate declined by 1/5. The friction coefficient of the Ni80Al20 coating was 0.5 and the Ni80Al20-MoS2 composite coating was 0.15, while the volume wear rate declined by 1/4 and 1/3.

The effects of ZrO2 nanoparticles in a NaAlO2 electrolyte on the thickness, morphology, composition, structure, and high temperature oxidation resistance of plasma electrolytic oxidation (PEO) coatings on a TC21 titanium alloy were investigated. The coating thickness increased with increasing concentration of ZrO2 nanoparticles in the electrolyte, accompanied by a decrease in the porosity of the coating surface. The PEO coatings formed in the ZrO2 nanoparticle-free electrolyte were composed of Al2TiO5. ZrTiO4, m-ZrO2, and t-ZrO2 were detected in the PEO coatings produced by the electrolyte that contained ZrO2 nanoparticles, which indicated that the deposition mechanism of the nanoparticles was partly reactive incorporation. The high temperature oxidation resistance of the TC21 titanium alloy at 650 &deg, C and 750 &deg, C was improved by 3&ndash, 5 times after PEO treatment. The oxidation mechanism involved oxygen diffusing inward to form an oxide layer at the interface of the PEO coating and substrate.

Barrier layer was prepared on TiAl alloy by Micro-arc oxidation(MAO) technique in silicate electrolyte, and cathodic plasma electrolytic deposition (CPED) technique was used to fabricate Al2O3 ceramic coating on prepared TiAl alloy in Al(NO3)3 (30 g/L) ethanol electrolytes with different water content by volume. Microstructure, composition and properties of coatings were analyzed, and mechanisms of different electrolytes were evaluated. The results showed that both arc-voltage and work voltage decreased with the increase of water content. Al2O3 CPED coatings were composed of deposition particles and cracks, and contained α-Al2O3 phase mainly and a small amount of γ-Al2O3 phase. The organic reaction mechanism was studied and the performance of TiAl alloy with CPED coating under 950 °C was superior to TiAl substrate.

Basic and ZrO2 doped composite plasma electrolytic oxidation coatings were prepared on the surface of TC21 titanium alloy. Subsequently, fretting wear tests of these two kinds of coated samples and the substrate alloy against GCr15 steel balls were conducted at 50 μm and 150 μm displacement amplitudes. The morphology, composition, valence states and topography of the fretting wear tracks were characterized and the wear mechanisms were studied. The results indicated that the porosity of the composite coatings was lower than that of the basic coatings, and the microhardness, adhesion strength and toughness were higher. When the fretting was in the partial slip regime (50 μm displacement amplitude), the fretting damage of the three materials was slight. Meanwhile, the cracks and delamination in the microslip zone of the TC21 alloy were not observed in the coated samples. When the fretting was in the slip regime (150 μm displacement amplitude), although the TC21 alloy and basic coatings experienced local wear, there was no significant material loss of the composite coatings, which demonstrated that the composite coatings could improve the fretting wear resistance.

In order to improve the oxidation resistance of TiAl alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373K for 1-3 hours. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on TiAl alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant (k) ranged from 1.53 mg2/(cm4·h2) to 2.3 mg2/(cm4·h2). Activation energy (Q) for the process was calculated as 109 kJ/mol, determined by Arrhenius' equation: k = k 0 exp[–Q/(RT)].

An innovative composite plating apparatus for complex-shaped cylinders has been proposed. It allows the cylinders not to be immersed entirely in the electrolyte. Using circulating-solution co-deposition (CSD) technique in the novel plating apparatus, Ni-SiC composite coatings can be deposited on the inner surfaces of cylinders, while the outer remains intact. It is of great significance for the engine cylinders whose outer surfaces require high precision to meet the need of specific functions and cannot be corroded by the electrolyte during electrodeposition. The morphology, structure, hardness, corrosion and wear resistance of the Ni-SiC coating in comparison with that of Ni coating have been analyzed. Characterization experiments reveal that the volume fraction of the deposition rate is about 83 μm/30 min. In comparison with pure Ni coating, Ni-SiC composite coating exhibits better anti-corrosion performance, higher hardness as well as greater wear resistance. The predominant wear mechanism for Ni-SiC is abrasive wear and oxidational wear. These results prove that the CSD technique is an efficient technology to prepare Ni-SiC composite coatings with excellent corrosion and wear resistance at a high deposition rate. The composite plating apparatus proposed for large-scale industrialization plan is worth to be highly recommended.

Oxidation behavior of a Ti2AlNb based alloy (Ti–22Al–23Nb (at.%)) and hot corrosion behavior of this alloy coated with a salt mixture of NaCl–Na2SO4 at 1023 K were comparatively investigated. The results showed that the alloy possessed relatively good oxidation resistance while suffered severe hot corrosion attack. The mass gain of the hot-corroded alloy was much larger than that of the oxidized alloy. The oxide scale was mainly composed of TiO2. During the oxidation, the oxide scale could keep intact. In the corrosion product scale, TiO2 + Al2O3 layers and NaNbO3 layers existed alternately and Al2O3 was distributed in the lower parts of the TiO2 + Al2O3 layers. The formation of the TiO2 + Al2O3 layer and the NaNbO3 layer should promote each other by altering the acidity/basicity of the salt film, and thus the growth of the scale was accelerated. The escape of the gaseous chlorides, the fast growth of the scale and the coefficient of thermal expansion (CTE) mismatch between TiO2 and NaNbO3 resulted in serious cracking and spalling of the scale.

To improve the fretting wear resistance of TC6 alloy, AT40 coating and Al2O3/AT40 composite coating were prepared on TC6 respectively by atmospheric plasma spraying (APS) technology. The microstructure, composition and adhesion strength of the two coatings were studied, and the fretting wear behavior of TC6 substrate and the coatings were investigated. The results showed that the two coatings were of lamellar stacked structures with holes and micro-cracks in stacked areas, and combined well with substrate. AT40 coating was composed of the Al2TiO5, Ti3O5 and α-Al2O3, and Al2O3/AT40 composite coating was formed by inner transition AT40 layer and outer Al2O3 layer. The inner transition AT40 layer had good compatibility with TC6 titanium alloy and Al2O3 layer, and the outer Al2O3 layer consists of α-Al2O3 and γ-Al2O3. The two coatings significantly improved the fretting wear resistance of TC6 alloy, and the fretting wear mechanism of the two coatings was fatigue wear and slight adhesive wear.

Linear friction welded joints of Ti2AlNb-based alloy were subjected to different solution and aging treatments. Relationships among solution and aging conditions, microstructural evolution and mechanical properties were investigated. The results indicate that the microstructures are very sensitive to solution conditions. In weld zone, the lath O precipitates at the grain boundaries when the joint is solution treated in O+B2 phase region, while the formation of lath α2 phase occurs in α2+B2+O phase region. In thermo-mechanically affected zone (TMAZ), aggregation of O phase and rim O phase resulted from further decomposition of α2 phase can be found during solution treatment. And after aging treatment, both weld zone and TMAZ are comprised of secondary acicular O phase within B2 grains. Solution and aging treatments have significantly enhanced the microhardness of weld zone due to the precipitation hardening of O phase and refined grain strengthening. After aging treatment, the tensile strength of the joints is further improved because of precipitation of secondary O phase, whereas, elongation is reduced due to the suppression of the hard deformation modes in fine acicular microstructures.

Linear friction welds of a Ti2AlNb-based alloy were subjected to post-weld heat treatment (PWHT) at 815 °C × 1 h (PWHT1) and at 1000 °C × 1 h + 815 °C × 2 h (PWHT2) followed by air cooling. The microstructure and mechanical properties of the joints under as weld and PWHT conditions were investigated. The results indicate that in the as weld joint, the weld zone mainly consists of B2 phase while the quantity of α2 and O phase is relatively small, and most O phase gradually turns into B2 phase when the amount of α2 phase reduces as well in thermo-mechanically affected zone (TMAZ). After PWHT1, O precipitates within recrystallized B2 grains can be found in weld zone and the decomposition of α2 phase caused by niobium diffusion is found in TMAZ. PWHT1 have significantly enhanced the mechanical properties due to the O phase precipitation hardening and refined grain strengthening. And the coarsening of the microstructure in weld zone under PWHT2 is evident, which consequently reduces the elongation. Keywords: Linear friction welding, Ti2AlNb-based alloy, Post-weld heat treatment, Microstructure, Mechanical property

Al2O3 coating was fabricated on the surface of γ-TiAl alloy via cathodic plasma electrolytic deposition (CPED) technique. The microstructure and the composition of the coating were elaborately characterized. The results revealed that, the uniform coating combined well with the substrate, which was mainly composed of α-Al2O3, γ-Al2O3 and trace amount of amorphous Al(OH)3. Moreover, the high temperature oxidation behaviors of the substrate, the coating and their interface were investigated in detail. It was found that the existence of the Al2O3 coating could substantially decline the oxidation rate of TiAl alloy, because of the significant increase in high temperature oxidation resistance.

Coatings were prepared by aluminization of a Si–Y co-deposition coating on a Ti2AlNb based alloy using halide activated pack cementation technique. The microstructure evolution and the high temperature oxidation behavior of the coatings were investigated. During the aluminization, the (Ti,Nb)5Si4 inner layer of the Si–Y co-deposition coating was consumed faster than the (Nb,Ti)Si2 outer layer. A (Ti,Nb)Al3 superficial layer and a (Nb,Ti)3Si5Al2 + (Ti,Nb)Al3 middle layer successively formed. Besides, (Nb,Ti)3Si5Al2 pieces appeared inside the outer layer when solid solution Al in (Nb,Ti)Si2 reached saturation. Both inward diffusion of active [Al] atoms and outward diffusion of Ti and Nb atoms controlled the coating growth. The outward diffusion of Ti and Nb atoms caused Al beneath the inner layer was enriched continuously. The Si–Y co-deposition + aluminization coating could provide better protection for the Ti2AlNb based alloy from oxidation at 1123 K than the Si–Y co-deposition coating, which was attributed to preferential formation of Al2O3 on the surface to prohibit formation of loose TiO2. After the oxidation for 100 h, a continuous, compact and adhesive oxide scale consisting of an Al2O3 main part and an Al2O3 + TiO2 + SiO2 lower part formed on the coating.

In order to improve the surface performance and increase the lifetime of P110 oil casing tube steel during operation, electroless plating was conducted to form Ni-P coating onto its surface. The surface morphology/element distribution and phase constitution of the Ni-P coating were analyzed using scanning electron microscope (SEM) equipped with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Tribological and electrochemical measurement tests were applied to investigate the wear and corrosion resistance of P110 steel and the Ni-P coating. The results showed that a uniform and compact, high phosphorous Ni-P coating was formed. The obtained Ni-P coating indicated certain friction-reduction effect and lower mass loss during friction-wear tests. The Ni-P coating also exhibited higher corrosion resistance in comparison with bared P110 steel. The obtained Ni-P coating has significantly improved the surface performance of P110 steel.

In the field of corrosion research, mass gain/loss, electrochemical tests and comparing the surface elemental distributions, phase constitutions as well as surface morphologies before and after corrosion are extensively applied to investigate the corrosion behavior or estimate the corrosion resistance of materials that operated in various environments. Most of the above methods are problem oriented, complex and longer-period time-consuming. However from an object oriented point of view, the corroded surfaces of materials often have self-similar characterization: fractal property which can be employed to efficiently achieve damaged surface analysis. The present work describes a strategy of comparison of the surface fractal dimensions for corrosion resistance estimation: chromizing coating was synthesized on P110 steel surface to improve its performance via pack cementation. Scanning electron microscope (SEM) was used to investigate the surface morphologies of the original and corroded samples. Surface fractal dimensions of the detected samples were calculated by binary images related to SEM images of surface morphologies with box counting algorithm method. The results showed that both surface morphologies and surface fractal dimensions of P110 steel varied greatly before and after corrosion test, but the chromizing coating changed slightly. The chromizing coating indicated better corrosion resistance than P110 steel. Comparison of surface fractal dimensions of original and corroded samples can rapidly and exactly realize the estimation of corrosion resistance.

Si–Al–Y co-deposition coatings were prepared on a Ti–Al alloy by pack cementation process at 1050 for 4 h. The effects of pack Y2O3 content (from 0 to 5 wt%) on the microstructure and constituent phases of the co-deposition coatings were studied, the wear resistance of the substrate and the coated specimens were also compared at 600 °C in air. The results showed that the pack Y2O3 content imposed strong influences on both coating structures and phase constituents. The coatings prepared with the pack mixtures containing 1 and 2 wt% Y2O3 were composed of an TiSi2 out layer, an (Ti, X)5Si4 and (Ti, X)5Si3(X represents Nb and Cr)middle layer, an TiAl2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi2,(Ti, X)5Si4 and (Ti, X)5Si3 in the out layer of the coating prepared with the pack mixture containing 3 wt% Y2O3. Moreover, (Ti, X)5Si4 and (Ti, X)5Si3 phases were observed in the outer layers of the coatings prepared with the pack mixtures containing 0 and 5 wt% Y2O3. The coating growth could be catalyzed obviously when the content of Y2O3 in the pack mixtures increased from 1 to 2 wt%, but this phenomenon was not observed when further increased the pack Y2O3 content to 3 or 5 wt%. Si–Al–Y co-deposition treatment improved the surface hardness and wears resistance of the Ti–Al alloy significantly. The wear resistance of the tested samples could be sorted in the following sequence: 1% Y2O3-coating > no RE-coating > bare Ti–Al alloy.

A chromizing coating was formed on P110 oil casing tube steel (P110 steel) via pack cementation to improve its performance and increase the lifetime during operation. The slurry erosion behaviors of the P110 steel substrate and the chromizing coating were assessed in a liquid-solid two-phase flow condition. The results showed that the obtained coating exhibited higher surface hardness, lower mass loss, and lower slurry erosion rate than those of P110 steel. The chromizing treatment has significantly improved the surface hardness and slurry erosion resistance of P110 steel.

A series of rare earth (RE) dispersed chromizing coatings were produced on P110 steel by pack cementation. The orthogonal array design (OAD) was applied to set the experiments. An artificial neural network (ANN) approach is employed to predict the thickness values of the obtained chromizing coatings based on the OAD tests results. The results revealed that the built model was reliable, the thickness values of chromizing coatings were well predicted at selected process parameters, and the predicted error lied in rational range.

Chromizing coating was fabricated on P110 oil casing tube steel by employ of pack cementation to improve the performance and increase the life-time during operation. Scanning electron microscope (SEM), X-ray diffraction (XRD), glow discharge optical emission spectroscope (GDOES) and microhardness tester were used to investigate the surface morphology, cross-sectional microstructure, phase constitutions, element distribution and microhardness distribution of the coating. Friction and wear behaviors of P110 steel and chromizing coating were measured using a ball-on-disc type tribometer under sliding against two counterparts in dry and wet conditions. The variations in friction coefficient, mass loss and surface morphologies of the tested samples were systemically investigated and analyzed. Energy dispersive spectrometer (EDS) and SEM were employed to elucidate the wear mechanisms of the tested samples. The results showed that the obtained coating was uniform and compact, mainly consisted of M x C y and reached a thickness of 55 μm. Chromizing coating had higher surface hardness and lower mass losses than that of P110 steel. When sliding against GCr15, chromizing coating showed no obvious friction–reduction effect, but indicated certain anti-friction property in sliding against Si 3 N 4 . The tested samples varied with surface hardness values and surface compositions have shown different wear mechanisms in the sliding tests. Chromizing treatment makes it possible to create on the working surface of P110 steel with enhanced surface hardness and wear resistance.

The protective chromium coating was prepared on P110 steel by employing pack cementation. The corrosion behaviors of P110 steel and the obtained coating in CO2-saturated simulated oilfield brine were studied by static complete immersion tests and electrochemical measurements. The corrosion attacks of the samples were determined by mass loss, corroded surface morphologies, corrosion products, and results of electrochemical measurements. The experimental results showed that the coating was uniform, continuous and compact. The chromium coating was slightly corroded, and the mass loss and corrosion rate of the coating were far lower than those of P110 steel. Chromium coating has higher self-corroding potential and lower corrosion current density than P110 steel in accordance with the electrochemical tests results. Taken as a whole, chromizing treatment has significantly improved the corrosion resistance of P110 steel.

In order to improve the corrosion resistance and increase the service lifetime of P110 steel during operation, four chromizing coatings were formed onto its surface with/without addition of rare earths via pack cementation process. The surface morphologies and microstructures of the chromizing coatings were observed using scanning electron microscopy (SEM), and the phase constitutions were investigated by X-ray diffraction (XRD). Electrochemical corrosion behavior of the chromizing coatings in simulated oilfield brine at 30 °C was studied by means of open-circuit potential measurements and cyclic potential dynamic polarization tests. The results showed that the coatings were mainly composed of Cr 23 C 6 , Cr 7 C 3 , and (Cr, Fe) 7 C 3 . There were obvious differences in surface morphologies and microstructures of the coatings. The thickness values of the coatings were arranged as follows: CeO 2 >-coating>Y 2 O 3 -coating>La 2 O 3 -coating>no RE-coating. The corrosion resistance of the coatings was sorted in the following sequence: CeO 2 2 O 3 -coating 2 3 -coating. Adding various rare earths could influence the microstructures and corrosion resistance of the chromizing coatings indeed.

In the comparison of the solidification characteristics of supercooling directional solidification (SDS) with constrained directional solidification (DS) and with the consideration of the inheritance of supercooled melt, the SDS technique established with the combination of melt supercooling and traditional DS was proposed. An exploring study on SDS techniques was also conducted using appropriate facilities, designed and manufactured by the authors' laboratory and the deep supercooling of Cu–5.0%Ni alloy, and its DSs were implemented.

The coercivity of anisotropic cast–hot‐pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation‐controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse‐grained cast structure.

In order to enhance the surface properties of P110 oil casing tube steel and increase its usage during operation, chromium coating was fabricated by pack cementation. Scanning electron microscope, energy dispersive spectrometry and X-ray diffraction were used to investigate the surface morphology, cross-sectional microstructure, element distribution and phase constitutions of the coating. Comparative examinations on corrosion resistance between chromium coating and 13 Cr stainless steel in CO2-saturated simulated oilfield brine were carried out via electrochemical measurements. The results showed that the obtained coating was uniform and compact, mainly consisted of CrxCyand doped with minor Cr2N . Chromizing treatment made it possible to create on the working surface of P110 steel with enhanced corrosion resistance, and the chromium coating indicated lower pitting corrosion sensitivity than that of 13 Cr stainless steel.

Oil casing tube is the foundation member of an oil well and it plays an important role in oil exploration and exploitation. The oil casing tubes are prone to failure induced by corrosion and wear during applications. Based on the fact that the damages caused by corrosion and wear are first generated on the surface of oil casing tube, adopting an appropriate surface treatment technology would be a promising approach to protect itself from deterioration. Surface treatments can fabricate protective layers with different composition or structure from the substrate. This paper reviewed the existing literatures about the protection of oil casing tube steel via surface treatment in China.

In order to enhance the surface properties of P110 oil casing tube steel and increase its usage during operation, chromium coating was fabricated by pack cementation. Scanning electron microscope, energy dispersive spectrometry and X-ray diffraction were used to investigate the surface morphology, cross-sectional microstructure, element distribution and phase constitutions of the coating. Comparative examinations on corrosion resistance between chromium coating and 13Cr stainless steel in CO2-saturated simulated oilfield brine were carried out via electrochemical measurements. The results showed that the obtained coating was uniform and compact, mainly consisted of CrxCy and doped with minor Cr2N. Chromizing treatment made it possible to create on the working surface of P110 steel with enhanced corrosion resistance, and the chromium coating indicated lower pitting corrosion sensitivity than that of 13Cr stainless steel.