Microstructures and properties of non-preheated hardfacing welding

A new type of non-preheated hardfacing electrode was developed using H08A as the core and the coat contents including ferrotitaninm, ferrovanadium, graphite, rutile etc. The microstrnctures and properties of hardfacing metal were systematically researched. The results show the hardness of hardfacing metal increases with increasing of ferrotitanium, ferrovanadium, graphite in the coat, but the crack resistance and processing weldability become worse. The carbides formed by arc metallurgic reaction are uniformly dispersed in the matrix structure. The phases of hardfacing metal consist of α-Fe, γ-Fe, VC, TiC and Fe3 C.The carbides are compression aggregation of TiC and VC, and their appearances present irregular block. The matrix microstrncture of hardfacing metal is lath martensite. The hardfacing layers with better crack resistance and wearability are achieved and no visible cracks occur when using non-preheated electrode in continuous welding process. Hardness of hardfacing metal is more than 60HRC, and its relative wearability is five times of wearability of D667 electrode in abrasive wear test.     

Effect of heat treatment on the microstructure and hardness of C-Cr-W-Mo-V-RE Fe-based hardfacing layer

After different heat treatment processes, the metal compound, the microstructure and the hardness of the C-Cr-W- Mo-V-RE Fe-based hardfacing layers are investigated by means of metallographic microscope, X-ray diffraction （ XRD ）, energy dispersive spectrum（ EDS ）, transmission electron microscope（TEM） and hardness tester. The results show that the hardfacing layers have higher tempering stability and secondary hardening property. After quenching at 820 ℃ ,the hardness value（ HRC37 ） and the microstructure of the layers are similar to that normalized at 820 - 1 000 ℃. The tempering stability and the hardness increases with increasing quench temperature, which is attributed to the amount of the alloy element in the matrix. These results are very helpful for improving the mechanical properties of the hardfacing layers.     

Development of new type of wear and crack resistant hardfacing electrode

By using H08A bare electrode and the coating fluxes of ferrotitanium, rutile, graphite, calcium carbonate and calcium fluoride, a new type of wear and crack resistant hardfacing electrode was developed. The microstructure and wear properties of deposited layer were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry(XRD) and wear test. The results indicate that TiC particles are produced by direct metallurgical reaction between ferrotitanium or rutile and graphite during welding process. TiC particles with sizes in the range of 3 - 5μm are dispersed in the matrix of lath martensite and retained austenite. The deposited layer of the new type of hardfacing electrode possesses better wear and crack resistance than that of D618 and D667 hardfacing electrodes.     

The mechanical measuring method of welding heat source efficiency

Based on the principle of residual deformation induced by superposition of the welding residual stress and working stress, the welding heat source efficiency has been determined by measuring displacement changes of specimens under loading and unloading in tensile tests, and combining with calculating welding parameters. Meanwhile, the welding heat source eficiencies obtained are compared with those of the measuring-calculating method. The research results show that the welding heat source efficiencies are almost the same as those obtained by the measuring-calculating method. Therefore, the welding heat source efficiency can be determined accurately by this method, and a new determining method of the heat source efficiency for the welding heat process calculating has been provided.     

Metallographic Characterization of the Microstructure of Tool Steels

Examination of selectively etched tool steel microstructures by light microscopy provides more information than standard etchants, such as nital, picral or Vilella‘s reagent. Further, the images are more suitable for quantitative measurements, especially by image analysis. Specimens must be properly prepared, damage free, if selective etchants are to be applied successfully. A number of etchants have been claimed to selectively etch certain carbides in tool steels. The response of these etchants has been evaluated using a variety of well-characterized tool steel compositions. While many are selective, they are often selective to more than one type of carbide. Furthermore, their use in image analysis must be evaluated carefully as measurements showed that the amount and size of the carbides are often greater after selective etching as many of these reagents outline and color or attack the carbides. Selective etching of the matrix, leaving the carbides unaffected works well, but no one etchant will cover the broad spectrum of tool steel compositions. No etchant has been found that will color retained austenite in tool steels and image analysis of retained austenite in tool steels are always much lower than by x-ray diffraction unless retained austenite is the dominant phase present in grossly over-austenitized steels.     

Influence of Electrolyte Composition on the Calcium-Phosphorus compound Coating on Titanium Substrate by Micro-arc Oxidation

In recent years the biomedical material has been widelydeveloped,and application that the implant materialssubstitute for hard organ has attracted much attention.Titanium alloys are frequently utilized as skeletonimplant and modification materials because of theirlight density,high strength and proper biocompatibility.However,titanium alloys are bioinertial materials,which are not beneficial to the performance of organiccoalescence,so they are not yet the ideal implantmaterials.Therefore,impro…     

Study of Carbon Contaminated Epitaxial Silicon

The properties of the carbon contaminated silicon epitaxial layer and its surface have been studied by means of JAMP-10Auger electron microprobe and JEM-2000FX transmission scanning electron microscope.The results show that the fog defectson the surface are due to carbon contamination.The existence of SiC in the silicon epitaxial layer has been identified by the elec-tron diffraction analysis.     

Research on Mediate Temperature Decomposition of High Nitrogen Austenite

The decomposed products from high nitrogen austenite aging at 225~C were investigated by TEM. It is found that the shape of decomposition products inside the austenite grains is not regular and not strictly oriented. Preferential nucleation of γ‘-FenN at dislocations and grain boundaries has been observed. It also has been found that during the first stage of the high nitrogen austenite decomposition a large quantity of ultra-fine γ‘-FenN precipitate inside the parent austenite, which has been thought to be the undecomposed region before. The ultimate products are composed of highly dispersed α-Fe and γ‘-Fe4N, with both of them maintaining nanometer scale. The micro-hardness of them can be as high as 900HV.     

The Splittings of p_± States in Infrared Spectra of Thermal Donors in Silicon

p -type CZ silicon crystals annealed at 450℃ have been investigated by low temperature infraredspectroscopy with high resolusion. It has been shown that the 2p± and 3p± bands of neutral thermal donorsTD~° are all split into two bands, which have not been reported before. In addition, the concentrations ofindi-vidual TD_i and total TD have been derived from the heights of 2po bands, and the boron concentrations de-rived from that of 320 cm~(-1) band. The room temperature resistivities of samples have been evaluated and thecomparison with practically measured resistivities have been made.     

Effects of Bond Parameters on Hydrogen Storage Capacity of Ti–V–Cr BCC Phase Alloys

The relation between the effective hydrogen storage capacity CH of Ti-V-Cr alloys and out-layer electrons, atomic diameter difference, electronegativity difference has been studied. It is shown that their relation can be expressed as TlnCH = 0.45922T＋5044.8 (DX)2＋1250.6δ2－285.80 n2/3. The factor of out-layer electrons has the largest effect on the CH of Ti-V-Cr alloys, while the factor of electronegativity difference has the smallest effect among the three bond parameters. The effective hydrogen storage capacity of Ti-V-Cr alloys is greater than 2.0wt% when n2/3 values of Ti-V-Cr alloys are between 1.98 and 2.14, d2 values are between 0.255 and 0.288 and (DX) 2 values are between 0.0638 and 0.0765     

First-principles calculation of phase equilibria and phase separation of the Fe-Ni alloy system

Theoretical investigation of the phase equilibria of the Fe-Ni alloy has been performed by combining the FLAPW total energy calculations and the Cluster Variation Method through the Cluster Expansion Method. The calculations have proved the stabilization of the LIE phase at 1：3 stoichiometry, which is in agreement with the experimental result, and predicted the existence of L1 0 as a stable phase below 550 K; this L1 0 phase has been missing in the conventional phase diagram. The calculations are extended to the Fe-rich region that is characterized by a wide range phase separation and has drawn considerable attention because of the intriguing Invar property associated with a Fe concentration of 65%. To reveal the origin of the phase separation, a P-V curve in an entire concentration range is derived by the second derivative of free energy functional of the disordered phase with respect to the volume. The calculation confirmed that the phase separation is caused by the breakdown of the mechanical-stability criterion. The newly calculated phase separation line combined with the L1 0 and L12Eorder-disordered phase boundaries provides phase equilibria in the wider concentration range of the system. Furthermore, a coefficient of thermal expansion （CTE） is attempted by incorporating the thermal vibration effect through harmonic approximation of the Debye-Gruneisen model. The Invar behavior has been reproduced, and the origin of this anomalous volume change has been discussed.     

Influence of RE elements on the performances of Ni-P coelectrodeposition bath

Through adding the chlorides of La and Ce into Ni-P coelectrodeposition bath, the effects of rare earth （RE） elements on the performances of the bath have been investigated by hull cell tests, far and near cathodes tests, and so on. It is shown that the optimum contents of CeCl3, LaCl3 and their mixture are all 2 g/L. The bright zones of the Ni-P coelectrodeposition bath are greatly widened by the addition of RE, and this effect is more obvious in the low current density range. By the addition of RE, the current efficiency of the Ni-P coelectrodeposition bath is greatly increased. The results also show that RE elements can improve the dispersing capacity of the bath. It can be theoretically deduced that RE ions improve the cathodic polarization degree of Ni-P codeposition. This deduction has been confirmed by the cathodic polarization curves measured in the baths.     

Formation of carbonitride precipitates in hardfacing alloy with niobium addition

Niobium, as the most effective second-phase forming element, was added in the Fe-Cr13-C-N hard-facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The ther-modynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb(C, N) precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condition, a large number of secondary carbonitrides can pre-cipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and inter-granular chromium depletion.     

Influence of microwave irradiation on the preparation of novolacs for the shell process

1. IntroductionThe shell process is unique in its ability to makeexcellent reproducible castings with better surface finishand dimensional accuracy than castings made of othersand processes. It is also simpler to operate than many ofother casting processes [1-3]. Therefore, it has been widelyused in the foundry industry and presents a promisingfuture. In recent years the application of shell process inChina has been greatly increased and novolacs consumedin this process are up to tens of thou…     

Study on intelligent welding mobile robot with the function of auto-searching weld line

The development of welding robots suitable for specially unstructured working enviroments has been become an important development direction of industrial robot application because large-scale welding structures have been used more and more widely in modern industry. In this paper, an intelligent mobile robot for welding of ship deck with the function of autosearching weld line was presented. A wheeled motion mechanism and a cross adjustment slider are used for the welding robot body. A sensing system based on laser-PSD （position sensitive detector） displacement sensor was developed to obtain two dimensional deviation signals during seam tracking. A full-digital control system based on DSP and CPLD has also been realized to implement complex and high-performance control algorithms. Furthermore, the system has still the function of auto-searching weld line according to the characteristics information of weld groove and adjusting posture itself to the desired status preparing for welding. The experiment of auto-searching welding line shows that the robot has high tracing accuracy, and can satisfy the requirement of practical welding project.     

Electronic structure of Au-Cu alloys

By studying the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the potential energy function, atomic volume interactive function and electronic structure of Au-Cu alloys have been determined. Then following the general Vegard‘s law in characteristic theory, the electronic structure and properties of disordered continue solid solution and three ordered alloys with the maximum ordering degree are calculated. It is found that the non-bonding electrons and near-free electrons in outer shell will transform to covalent electrons during alloying. By analyzing the variation of electronic structure and cohesion of ordering and disordered alloys, the transformation of order-disorder transition Au-Cu alloy has been studied.     

Effects of Ce and Ti on the microstructures and mechanical properties of an Al-Cu-Mg-Ag ahoy

The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg-Ag alloy, increase the nucleation ratio for Ω phase as heterogeneous nucleation centers, inhibit the growth of Ω phase during aging, and thus increase the volume fraction and decrease the spacing of Ω phase. These microstructures increase the yield strength and tensile strength. However, if both Ce and Ti are added to the alloy, they form （Ce,Ti）-contained compounds and increase the grain size during casting, but have no effects on the nucleation and the growth of Ω phase during aging. The alloy containing both Ce and Ti has a relatively lower Vicks hardness and strength compared to the alloy containing either Ce or Ti.     

高耐磨药芯焊丝堆焊组织及基体选择

制备了高铬铸铁型自保护药芯焊丝,并采用此焊丝分别在 Y-Ni4 铸铁、65Mn钢、40Cr 钢和灰口铸铁基体上进行堆焊.对不同堆焊试样进行硬度测试,对堆焊金属及其结合部位进行显微组织及断口形貌观察.结果表明,堆焊金属硬度在 60HRC 以上,断裂方式均为解理断裂.65Mn 钢堆焊试样熔合较好,且基本无裂纹,可在受冲击载荷较大的条件下使用;Y-Ni4 铸铁堆焊试样熔合良好,但在热影响区存在裂纹,应在冲击载荷较小或不受冲击载荷条件下使用;40Cr 和灰铸铁堆焊试样熔合不好,熔合区存在许多缺陷,不宜作为耐磨堆焊基体材料.

Abstract：

Four matrix materials, Y-Ni4 cast iron, 65Mn steel, 40Cr steel and grey cast iron, were hardfaced by the high chromium cast iron of self-shielded flux-cored wire separately. The hardness of different hardfacing specimens was measured, and the microstructures, fracture morphologies and the binding sites of different hardfacing specimens were observed. The results show that the hardness of the hardfacing metal is over 60 HRC and the fracture is of cleavage type. The fusion zones of 65Mn and Y-Ni4 hardfacing metal are good ones. However, the cracks can be observed in the heat-affected zone of Y-Ni4 hardfacing specimen. Therefore, the hardfacing metal of 65Mn steel is suitable for the condition of high stress wear and Y-Ni4 cast iron is suitable for the lower one. Besides, there are many defects in the fusion zone of 40Cr and grey cast iron hardfacing specimens, which are not suitable for the wear resistant matrix materials.     

Diddusion bonding of titanium alloy to tin-bronze

The vacuum diffusion bonding of titanium alloy to tin-bronze has been studied and the feasibility and appropriate processing parameters have been investigated.The maximum tensile strength of the joints is 168MPa,and a firm joint is obtained.The microstructure of diffusion bonded joint has been observed by SEM.X-ray and EPMA,and the main factors affecting diffusion bonding have been analyzed.The intermetallic compounds Ti2Cu and TiCu were formed near the interface.The width and quantity of the intermetallic compound increases with the increase of the bonding time.The formation of the intermetallic compounds results in embrittlement of the joint and the poor joint properties.     

Degradation of crystal violet using nanometer TiO2 under the synergistic action of H2O2 and ultrasonic wave

TiO2 nanoparticles with different phases are prepared by hydrolysis of titanium tetrabutoxide in the presence of HCl. The composition and microstructure of the resulting samples are studied by XRD and TEM. These results show that the range of particle size of TiO2 is from 20 to 30 nm. The mechanism of TiO2 photocatalysis reaction has been discuss edextensively. Photocatalyfic activities of nanometer TiO2 are also evaluated by degradation of the crystal violet solution. Experimental results indicate that the synergistic action of H2O2 and ultrasonic wave greatly enhances photo-catalytic reaction of TiO2.