Qing Jun Chen

Effect of Corrosive Medium on the Corrosion Resistance of FeCrMoCB Amorphous Alloy Coating

The purpose of this study is to investigate the electrochemical properties of Fe44Cr16Mo16C18B6 amorphous alloy coating fabricated using high velocity oxygen fuel (HVOF) technology in 2.0M HCl and NaOH solution at room temperature(25°C). Based on the potentiodynamic polarization curves and Electrochemical Impedance Spectroscopy(EIS) testing results of coating in aqueous solutions of HCl and NaOH, the corrosion resistance of Fe44Cr16Mo16C18B6 amorphous alloy coating in HCl solution was superior to that in NaOH solution. The icorr was 1.487×10-5A·cm-2 in HClsolution and 1.107×10-4A·cm-2 in NaOH solution, while the Rt reach to 5.789×104Ω·cm2 and 9780Ω·cm2, respectively. On the other hand, these corrosion phenomenon could be better interpreted by R(Q(R(RQW)))(RL) and R(RL)(Q(R(CW))) equivalent circuit model, which were different from that of other Fe-based amorphous alloys in HCl and NaOH solution, respectively.

Study on Salt Fog Corrosion of FeCoCrMoCBY Amorphous/Nanocrystalline Alloy Coating

Fe-based amorphous alloy coating with a composition of Fe41Co7Cr15Mo14C15B6Y2 was prepared by high velocity fuel(HVOF) technique. The influence of heat treatment on crystalline behavior, the phase structure and corroded morphology of the coating was investigated by Differential Thermal Analysis(DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy(SEM), respectively. The experimental results indicate that the amorphous alloy coating exhibited a two-step crystallization process with crystallization peak temperature at 698°C and 822°C, respectively. Amorphous coating exhibits excellent corrosion resistance than that of the corresponding nano-crystalline coating with heat treatment at 700°C for 2h, 8h and 12h. Furthermore, the nano-crystalline coating annealed 700°C for 12h suffers slight homogeneity corrosion, which did not exhibit obvious pitting on comparison with coating holding 2h and 8h.

Thermal Expansion Behavior and Characteristic of SiCp/Al Composites

SiCp/Al composites were fabricated by ceramic mold freedom infiltration and pressureless infiltration, respectively. The microstructure and phases are analyzed by metallurgical microscope and coefficient of thermal expansion of SiCp/Al composites were tested by thermal dilatometer. The results show that SiCp/Al composites are compact and uniform. SiC particles were dispersed uniformly in Al matrix, and SiCp segregation was not found in composites. Under a certain SiCp size range, space between SiCp decreases with decreasing of SiCp size, and CTE of SiCp/Al composites also decreases with decreasing of particles size. Compared with CTE of composite with pure aluminum as matrix, CTE of composite with ZL101 as matrix is less. Under the annealing process, CTE of SiCp/Al composites with ZL101 as matrix is less than that with the solution and aging, which indicated that its dimensional stability of resisting to temperature fluctuation is better, and thermal expansion behavior and characteristic of SiCp/Al composites are also better.

Microstructure and Property of the New Type White Cast Iron

The influences of the different Si (0.723%~4.5%) and Cr (2.0%~8.0%) contents on the microstructures and properties of Cr-Si-Mn white cast iron were investigated. It is shown that with increasing of amounts of Si and Cr elements, carbide undergoes an evident change in the morphology from the continuous net to isolated stripe and becomes clearly finer, even forms chrysanthemum-like microstructure which is usually found in high Cr white cast iron. Additionally, the amounts of the carbides increase too. The XRD analysis shows that the carbides are a mixture of Fe3C and Fe7C3 phases. Furthermore, the hardness of carbide and matrix is also found to progressively increase with increasing of amounts of Si and Cr elements. The hardness of the matrix in as-cast white cast iron is over HV400, suggesting that the matrix consists of martensite and bainite phases. The impact toughness of the samples declines evidently when Si content excesses 3.0wt%. It is also revealed that the bainite matrix in the Si-Cr white cast iron has a higher impact abrasive wear resistance than others, which is almost not dependent upon heating temperature and cooling rate. When Cr content approaches 5wt%, the impact wear resistance of the new cast iron is comparable to that of the traditional high Cr cast iron.

Salt Spray Corrosion Performance Associated with the Glass Forming Ability of the FeCo-Based Bulk Metallic Glasses

For the bulk amorphous Fe24+xCo24-xCr15Mo14C15B6Y2(X=0, 2, 4, 6 and 17) alloy, the corresponding corrosion properties associated with glass forming ability (GFA) have been carried out. Neutral salt spray corrosion test results show that the Fe28Co20Cr15Mo14C15B6Y2 alloy has the minimum corrosion rate, followed by Fe26Co22Cr15Mo14C15B6Y2, Fe24Co24Cr15Mo14C15B6Y2, Fe30Co18Cr15Mo14C15B6Y2, Fe41Co7Cr15Mo14C15B6Y2 and Ti6Al4V alloys. Specifically, the Fe28Co20Cr15Mo14C15B6Y2 alloy with the highest GFA also has the best corrosion resistance. With the increasing of Co addition, the corrosion resistance of the FeCo-based bulk metallic glasses is first increases and then decreases, which has the same trend of GFA with the change of Co elements. Furthermore, corrosion morphology are different for FeCo-based BMGs with different Co content.

Effects of High Co Contents in Fe-Cr-Mo-C-B-Y Alloy on the Glass Forming and the Mechanical Properties

A series of wedge shape Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) samples were prepared by copper mold suction casting method. The effects of high Co contents on glass forming ability (GFA) and mechanical properties of Fe24+XCo24-X Cr15Mo14C15B6Y2 bulk metallic glasses (BMG) were investigated, respectively. The glass forming ability of bulk amorphous Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) and Fe41Co7Cr15Mo14C15B6Y2 alloys have been researched. Simultaneously, the thermal conductivity parameters of those alloys were tested. The maximum thickness of amorphous region of wedge-shaped samples are dm =7.80 mm for Fe28Co20Cr15Mo14C15B6Y2, dm =7.10 mm for Fe41Co7Cr15Mo14C15B6Y2 and the thermal conductivity are λ=7.11 w.m-1.k-1 and 7.19 w.m-1.k-1, the thermal diffusivity are α=1.875 mm2/s and 1.905 mm2/s for Fe28Co20Cr15Mo14C15B6Y2 and Fe41Co7Cr15Mo14C15B6Y2 BMGs, respectively. The glass forming ability of Fe28Co20Cr15Mo14C15B6Y2 alloy is bigger than that of well known Fe41Co7Cr15Mo14C15B6Y2 alloy. With the change of Co content, the Vickers hardness of Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) change from 1292 to 1322Hv.

Study on Micro-Deformation Behavior of Sicp/Al Composites at Low Stress

In this paper, SiCp/Al composites were fabricated by spontaneous infiltration technology. The micro-deformation behavior (MDB) of low tress in some silicon carbide particulate reinforced aluminum composites (SiCp/Al composites) was investigated experimentally. The microstructure, micro-deformation of samples was analyzed by OM and WDW-50 respectively. The results show that, in aluminum matrix with incorporating SiCp, the distribution of SiCp was uniform. In the same other conditions, SiCp size of the composite plays an important role on MDB at low stress, and the micro-deformation performance of the SiCp/Al composite increases with decreasing of SiCp size. MDB of composites at low stress deeply depends on the matrix material, and MDB increases with increasing of the matrix strength. It was also found that, the micro-deformation of SiCp/Al composite was negative value in the early stages of low tensile stress, and the phenomenon can be explained by strain relaxation.

Electrochemical Behavior of Fe-Cr-Mo-C-B Amorphous Alloy Coating in HCl Solution

The corrosion behavior of Fe44Cr16Mo16C18B6 amorphous alloy coating was studied by electrochemical polarization curves and electrochemical impedance spectroscopy (EIS) in different HCl concentration solution at room temperature. Experimental results show that the polarization curves of the coating present a wide passivation range under open circuit potential and icorr increase from 1.049×10-5A/cm2 to 1.487×10-5A/cm2 with HCl solution from 0.5M to 2.0M. The EIS of coating are composed of high-frequency inductive loop and low-frequency capacitance arc, which is different from the EIS of other amorphous alloys, the Rt is up to 5789Ω·cm2 in 2M HCl solution. The especial equivalent circuit model R(RL)(Q(R(QRW))) can better interpret the corrosion behavior of the amorphous alloy coating.

Electrochemical Corrosion Behavior of Different Heat-Treatment Temperature Fe-Based Bulk Amorphous Alloy

Abstract: Fe41Co7Cr15Mo14C15B6Y2 (at%) bulk metallic glass was prepared by copper mold casting. Nano-crystalline Fe41Co7Cr15Mo14C15B6Y2 alloys were obtained by annealing. The influence of heat treatment at different temperatures in the alloy microstructure was identified by X-ray diffraction (XRD), and a comparative study of the electrochemical corrosion behaviors of amorphous and amorphous/nanocrystalline alloys was performed by potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) in 1.5M HCI solution, and the corrosion morphologies of the samples were observed by scanning electron microscopy (SEM). The results show amorphous alloy plays excellent anti-corrosion ability than that of the heat-treated samples, and the anti-corrosion ability of amorphous/nanocrystalline alloys decrease with the increasing of heat-treatment temperature.

Effect of Temperature on Structure and Corrosion Resistance of Oxide Scale on Hot Rolled Strip

Various structure scales at the surface of SS400 hot rolled strip were fabricated by heat treatment processes involving different temperatures. A simulation about the effect of various temperatures on the oxide scale structure during the coiling process was carried out. The structure and corrosion behavior of different oxide scales formed at the surface of hot rolled strip were investigated in sodium bisulfite (NaHSO3) solution by scanning electron microscope (SEM), X-ray diffraction (XRD), polarization curves and electrochemical impedance spectroscopy (EIS). The scale prepared at 550 °C is mainly composed of one layer of Fe3O4 phase. The scales prepared at 600 °C and 700 °C consist of the outer thin Fe2O3 layer and the inner (Fe3O4+Fe particles) layer. The scale prepared at 650 °C is mainly composed of Fe3O4 phase as well as a spot of Fe2O3 phase. The thickness of scale prepared at 650°C is observed to be more homogeneous than that of other scales and the bonding between the scale and substrate is found to be very strong. The experimental results clearly reveal that the hot rolled strip with scale prepared at 650 °C exhibits the most excellent corrosion resisting property in 0.01 mol/L NaHSO3 solution.