Zheng Jun Liu

Comparison of Microstructure and Properties of Ni-Based Overlay Deposit under Longitudinal Magnetic Field and Transverse Magnetic Field

plasma arc sufacing； magnetic field style ；Ni-based alloy；microstructure and properties Abstract. The Ni60 alloy was overlaid on low carbon steel by plasma arc surfacing with Longitudinal magnetic field or transverse magnetic field. The magnetic field current and surfacing current could been changed during surfacing. After plasma arc surfacing with magnetic field, the XRD, wear loss tes, micro-hardness test were used to analyze the effect of magnetic field style on properties of overlay deposit. The acting mechanism of magnetic field style and parameters on properties and microstructure of overlay deposit was researched. The results indicate that longitudinal magnetic field and transverse magnetic field all can improve the properties of overlay deposit, but give little effectives intervention to the process parameters. The active effect of transverse magnetic field is better than longitudinal magnetic field because of transverse magnetic field can make the microstructure finer, component more uniform.

In situ Synthesis of Ceramic Phase Reinforced Fe-Based Alloy Surface Coating by PTA

The in-situ ceramic phases reinforced Fe-based surface coating had been produced by prepared high-carbon ferrochromium, ferrovanadium and graphite power on 20g steel through plasma transferred arc weld-surfacing process(PTA). The microstructure and properties were investigated by means of optical microscopy(op), scanning electron microscopy(SEM), X-ray diffraction(XRD) and microhardness meter. The results showed that the substrate and the coating formed good metallurgical bonding.The microstructure of coating consists of primary M7C3 carbide and eutectic structures[M+γ′+M7C3+VC]. The primary hexagonal (Fe,Cr,V)7C3 with larger size evenly distributed in coating and the fine VC particles were globular shape. The microhardness appeared reasonable distribution from substrate to the top ,which ensured that the materials had good abrasive wear resistance.

Influence of Heat-Treatment on High-Phosphorus Ni–P Plating Coating

The high-phosphorus electroless Ni–P plating coating with 11.64 at.% was prepared by electroless technology. By means of x-ray diffraction and scanning electron microscopy, the morphologies and phase structures of coating were analyzed. Furthermore, the mechanical properties of coating were studied by micro-hardness tester and universal friction-wear testing machine. The results reveal that, with increasing heat-treatment temperatures, the hardness and the wear resistance of the coating are enhanced increasingly. Treated by 1 hour at 500 oC, the hardness and the wear resistance both display a optimum value, i.e. 1004 HV and 1.5×10-3g, respectively. The thermal shock test suggests that between coating and matrix exist a perfect cohesion.

Effect of Heat Input on Structure and Mechanical Properties of Low Matched Welded Joint in a 1000MPa Grade Steel

In order to investigate the effect of heat input on the microstructure and mechanical properties of low matched high-tensile steel welded joint, the metallurgical structure and mechanical properties of welded joint obtained with different heat input were analyzed using optical microscope , welded joint tensile test and impact test of weld metal. The results show that the optimal values are obtained when the heat input is 11.9KJ/cm,where the tensile strength is 798.45MPa and ballistic work is 69J; Weld metal microstructure is mainly composed by the primary ferrite and acicular ferrite. The width of the dendrite and grain size of the weld metal microstructure increase with the increasing of the heat input.

Microstructure Characteristics of Fe-xCr-C Hardfacing Alloys

A series of Fe-xCr-C hardfacing alloys were successfully fabricated on a substrate of 20g steel by gas tungsten arc welding (GTAW) process. These claddings were disigned to observe hypoeutectic, near-eutectic, and hypereutectic structures with various Cr3C2 and M7C3 carbides at room temperature. According to X-ray diffraction(XRD) and optical microscopy (OM), the hypoeutectic and eutectic composites include the Fe-Cr solid solution(α+A) and Cr3C2 carbides. Hypereutectic structures consist of α+A+M+M7C3 respectively. The cladding of hypereutectic microstructure with great amounts of primary M7C3 carbides had the highest hardness of the all conditions.

Microstructure and Wear Properties of Fe-Based Alloy Hardfacing Layers

The in-situ M7C3–TiC carbides reinforced Fe-based hardfacing coating had been produced by prepared high-carbon ferrochromium, ferrotitanium and graphite power on 20g steel through GTAW. The microstructure and hard phases morphology were investigated by means of OP, SEM and XRD. The results showed that the microstructure of hardfacing coating consists of lamellar martensite, TiC particles and M7C3 complex carbides. The TiC particles with flower-like shape and M7C3 complex carbides with hexagonal shape are observed in the coating. The hardfacing coating reinforced by M7C3 –TiC carbides revealed higher wear resistance than that of the substrate due to the presence of a high volume fraction of hard and wear-resistance primary M7C3 carbide uniformly distributed in the fine and strong [M+M7C3+TiC] eutectics matrix.

Investigation on High-Phosphorus Electroless Ni–P Plating Technology of Stainless Steel

The high-phosphorus electroless Ni–P plating was coated on the surface of stainless steel. Five parameters, which have much effect on coating quality, were chosen to optimize the high-phosphorus electroless Ni–P plating technology in L16(45) orthogonal test. By means of x-ray diffraction and scanning electron microscopy, the morphologies and phase structures of coating were analyzed. Furthermore, the mechanical properties of coating were studied by micro-hardness tester and universal friction-wear testing machine. The results reveal that the optimal technical parameters are as follows: 20 g•L-1 for NiSO4, 23 g•L-1 for NaH2PO2, 15 g•L-1 for C6H5O7Na3•2H2O, 8 g•L-1 for H2N-CH2-COOH, 10g•L-1 for CH3COONa, 7 g•L-1 for C4H6O4, with PH value of 4.6, which leads to perfect coating quality. Besides, the P content is 11.64 wt.%, i.e. a high-P coating. The micro-hardness of the coating is 550.67 HV and the wear loss, 4.7×10-3 g. The thermal shock test suggests that between coating and matrix exist a perfect cohesion, which is due to the homogenous and compact coating, with an amorphous structure, under the condition of the optimal technical parameters.

Effect of Magnetic Field on Microstructure and Properties of Magnesium Alloy Welded Joint with GTAW

In this investigation, in order to research the influence of magnetic field on microstructure and properties of magnesium alloy welded joint, the AZ31 magnesium alloy plates which was 5mm were welded by GTAW under longitudinal magnetic field. The tensile test, hardness test and SEM were taken place to analyze the properties and microstructure of welded joint under different magentic field parameters. The acting mechanism of magentic field on welded joint was studied. The results show that: External magnetic field can improve the properties of magnesium alloy welded joint which is welded by GTAW. The optimal mechanical property will be obtained when Im=2, f=20Hz, which the ultimate tensile strength is 231Mpa and the micro-hardness is 76.2HV.The magnetic field can produce electromagnetic stirring, which can refine crystal grain through breaking the pine-tree crystals with proper magnetic field current and frequency. The properties of welded joint will been improved by these fine crystal grain.

Effect of Magnetic Field Frequency on Microstructure and Properties of AZ31 Magnesium Alloy Welded Joint with GTAW

In this investigation, in order to research the influence of magnetic field frequency on microstructure and properties of magnesium alloy welded joint, the AZ31 magnesium alloy plates which was 5mm were welded by GTAW under longitudinal magnetic field. The tensile test, hardness test and SEM were taken place to analyze the properties and microstructure of welded joint under different magentic field frequency. The acting mechanism of magentic field on welded joint was studied. The results show that: External magnetic field can improve the properties of magnesium alloy welded joint. The optimal mechanical property will be obtained when Im=2, f=20Hz, which the ultimate tensile strength is 231Mpa and the micro-hardness is 76.2HV.The magnetic field can produce electromagnetic stirring, which can refine crystal grain through breaking the pine-tree crystals with proper magnetic field current and frequency. The properties of welded joint will been improved by these fine crystal grain.

The Effect of Cr on the Microstructure and Wear Resistance of Fe-Cr-V-C Hardfacing Alloys

Fe-Cr-V-C hardfacing alloys of three different Cr contents were produced by GTAW. The microstructure and hard phases morphology were investigated by means of OP, SEM and XRD. The results showed that the microstructure of hardfacing alloys consists of lamellar martensite, retained austenite, ferrite, VC particles and (Fe,Cr,V)7C3 complex carbides. The VC particles with exploded, globular shape and (Fe,Cr,V)7C3 complex carbides with interrupted netted, hexagonal shape are observed in the alloys.The amount of Cr affect the microstructure and wear resistance of the hardfacing coating. The volume fraction of (Fe,Cr,V)7C3 complex carbides increase as the Cr content increase. When the Cr content reached 22%, a multitude of hexagonal (Fe,Cr,V)7C3 complex carbides and a small amount globular VC particles are distributed in the softer ferrite and austenite matrix which ensure the high wear resistance.