Key Engineering Materials Vol. 814

Abstract: Wire electrical discharge machine (WEDM) is non-conventional machining process. It can be used for hard cutting material. The study has been presented the combining WEDM with an ultrasonic machine (USM) with brass and tungsten were used as a wire electrode and workpiece respectively. The experiment was carried out with an ultrasonic transducer at 40, 80 kHz. The results were observed with the material removal rate (MRR) and surface roughness (Ra). This research introduced the method of USM setup and described the effected of vibration with the wire electrode on the displacement of amplitude. The result shows that the WEDM process with USM at 40 kHz can be more improved with the material removal rate and surface roughness than that of USM at 80 kHz. This can be explained that higher frequency affected to vibration displacement which makes lower amplitude.

Abstract: Using ABAQUS finite element analysis software, the bending model of TC4 titanium alloy was established to study the stress distribution and obtain the maximum compressive displacement by limiting its yield strength. Therefore, the applicable properties of the materials are evaluated to provide a basis for material optimization.

Abstract: In this paper, SKD11 steel wire has been deposited on Cr12MoV plate using Nd: YAG pulsed laser for repairing the die surface damage. The effects of laser power, wire feeding speed, scanning speed and surface roughness on clad geometry have been studied with OM and LSCM. hardness distribution of the cladding layer is also obtained by microhardness tester. Experiment results indicate that the surface roughness is important for clad characteristics due to the light trapping effect. With the increases of roughness, the laser absorption ratio can be raised, both the clad depth and the dilution rate increase, the height decreases. The essence of influence mechanism is effective body energy Ev and specific filling rate ω, and can be used as critical process factors. When Ev is 80~100 J/mm³ and ω is 1~3, a flat cladding layer can be obtained with low dilution, less fusion defects and high hardness. Keywords: Cr12MoV, laser cladding with wire, surface roughness, clad geometry, hardness

Abstract: Cerium conversion coatings were obtained by immersing hot-dip galvanized steel (HDG) sheets in a cerous nitrate solution. The surface morphologies were observed with scanning electron microscopy. The composition of the coating were determined with X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy. The results showed that the modified cerium conversion coating grows more quickly than that of common cerium conversion coating. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements revealed that the corrosion resistance of the modified cerium conversion coating was superior to that of common cerium conversion coating and was comparable to that of the conventional chromate passivation coating.

Abstract: In recent years, environments of bearings and polymer materials have been more and more attractive due to several advantages against ordinary metal material. However, there is still room for the further study about strength of polymer bearings. One of questions is the mechanism of fatigue crack propagation, which is the main cause of the damage of polymer bearings under rolling contact with lubricant, like water. In this study, subsurface stress distribution and failure of PPS thrust bearings under rolling contact fatigue in water are discussed to understand the detail of the crack propagation.

Abstract: The high temperature creep test of heat-resisting steel 30Cr25Ni20 for automobile exhaust manifolds was carried out, and the creep strain-time curves at 650°C and 700°C in the different loads were obtained. The effects of different creep temperature and stress on creep life of materials were studied. The microstructure of the fracture after creep was observed by scanning electron microscopy. Microstructures before and after creep at different temperatures were compared by optical microscopy. The results show that the creep fracture life of heat-resistant steel decreases with the increase of stress at the same temperature. The creep fracture life decreases with the increase of temperature at the same stress, too. The fracture of heat-resistant steel shows good high temperature plasticity and a ductile fracture after creep. The fracture dimples become deeper with the increase of stress. At 650°Cand 700°C, the stress exponent is 8.6 and 6, respectively. When the sample was subjected to high temperature creep at 700°C, the precipitates increase obviously and the reticular structure became very large. At this point, the internal structure of the material is destroyed, and the matrix structure becomes unevenly distributed. The failure of the internal structure leads to the dramatic increase of the creep strain, and the failure of the internal structure will be more serious with the deformation of the sample.

Abstract: The fatigue tests were carried out under two kinds of hole-making technology, forming EDM and high-speed EDM. The hole taper and fracture surface of the sample were compared and analyzed. The finite element model with hole taper was established and the influence of the hole making technology on fatigue life was analyzed. Three conclusions have been obtained:First, the inner surface of the hole of the formed EDM is relatively flat, the residual deposit formed during the processing is less. and thickness of the recast layer and the content of oxygen are also lower than the high-speed EDM. Second,The fracture surface of the formed EDM shows obvious crack source, while the high-speed EDM has no crack source, and the area of the crack propagation area of the high-speed EDM is obviously larger. Third,the high-speed electric spark machining has obvious taper, under the load condition, the stress at the large hole end is higher than that at the small hole end, and large strain and damage are generated at the same time, resulting in crack initiation at the end of the large hole.

Abstract: In order to prevent the cold cracking of the welded joints and the overheating of the heat affected zone of the welded joints of the heavy and heavy parts of low alloy high strength steels, We have carefully studied the welding materials and methods for heavy parts of alloy high strength steel. We should pay attention to the preparation before welding, strictly control welding energy parameters, temperature parameters and operation parameters, adjust welding line energy and preheating temperature, control welding heat cycle, and adopt appropriate post-weld heat treatment and post-weld inspection process measures. By improving and optimizing the welding technology of heavy and heavy parts of low alloy high strength steel, we can effectively avoid the cold crack and overheating of heat affected zone in the welding of heavy and heavy parts of low alloy high strength steel, and greatly improve the mechanical properties of welded joints.

Abstract: The fatigue crack growth rate is the most important factor in predicting the life of a product when applying the damage tolerance design concept. Studies related to pure mode I for structures under fatigue loading have been actively conducted, while not many studies are conducted on the mixed mode. In this study, therefore, mixed mode fatigue crack growth experiments were designed using the Compact-Tension-Shear (CTS) specimens and the loading devices, proposed by Richard. Furthermore, the finite element analysis was used in determining the stress intensity factors of CTS specimen. As the results, the fatigue crack growth rate using the equivalent stress intensity factors proposed by previous researchers was lower than that of pure mode I at the initial stage of crack growth when the load angle increases.

Abstract: In order to realize the gasification dephosphorization process in converter slag splashing stage for avoiding the P enrichment, and the dephosphorized slag can be left for recycling in subsequent furnaces. The experiment of reduction of converter slag by coke powder in laboratory was carried out, The results show that with the increase of the experimental temperature, the gasification dephosphorization rate of coke powder gradually increases, and the gasification dephosphorization rate reaches up to 82.35% at 1900K. The gasification dephosphorization rate decreases with the increase of slag basicity. When the coke powder is added in a sufficient amount, increasing properly the FeO content of slag is favorable for the gasification dephosphorization reaction; when the coke particle size is between 0.5 and 2.5 mm, the gasification dephosphorization rate changed little, about 58%, but when the coke particle size between 2.5 and 3.5mm, the gasification dephosphorization rate dropped to 52%. The results provide some theoretical guidance for industrial development.