Solid State Phenomena Vol. 331

Abstract: The article’s primary purpose is to give a technological assessment of manufacturing complex-shaped parts using powder metallurgy. The process is considered in the example of a complex-shaped product consisting of several elements manufactured separately from the Fe-C-Cu powder mixture and then combined into a single structure. The joining was carried out by impregnation of porous structural elements with the fusion of copper-containing material. It has been demonstrated that the infiltration process is affected by many factors: porosity of structural elements, wettability of their pore channels, fluid flowability of the infiltrating material, and other factors. The research was carried out on the mass products - centrifugal pump stages for oil production. The elements compaction was carried out on hydraulic press at a pressure of 500 MPa, which ensured the average density of the parts after sintering up to 7.8-8.4 g/cm³. During sintering and impregnation, various types of defects of the pieces were detected, which were caused by the excessive thickness of the infiltrating material, different densities of the walls, and insufficient wettability in the connection zones of the elements.The investigations have shown that manufacturing complex components by prefabricating single elements and their subsequent sintering combined with infiltration is feasible. It can be done in a chamber furnace as well as with belt sintering. However, it is necessary to carefully prepare the mold before sintering, choose the infiltrating agent, and analyse possible disadvantages.

Abstract: A numerical simulation model has been established to obtain the deformation, strain and stress concentration of slab narrow side. The simulated temperature profiles of slab show a agreement with the results of measured temperatures by using infrared thermal camera. Moreover, the deformation, stress and strain of the slab have been investigated systematically, especially at the slab narrow side along the thickness direction. The relationship between the reduction amount and deformation, stress and strain concentration of slab narrow face has been investigated.

Abstract: In casting of Al-Mg alloy, especially in the aluminum alloy with high Mg content of more than 4 wt.% Mg, some cold cracks were found in last freeze of the flat ingots. The depth of cracks was bigger than 200 mm. The size of scrap removal of ingot was thus increased by 70 mm or more, and the yield of the flat ingots was greatly affected. Air cooling time of more than 20 min after casting was a better to reduce cracks in last freeze of Al-Mg alloy flat ingots.

Abstract: In order to improve the plasticity of the Al–Mg alloy, which fabricated by continuous casting and rolling, the alloy was heat treated at 370 °C, 400 °C, 430 °C and 460 °C for 2 hours and cooled with the furnace. The microstructure and mechanical properties of heat-treated Al–Mg alloy under different heat treatment temperatures were analyzed. The results show that the columnar grains begin to disappear at heat treatment temperature of 460 °C. The size of equiaxed grains begins to increase as the heat treatment temperature increases. The tensile strength of the alloy decreases with the increase of heat treatment temperature and the Brinell hardness increases when the heat treatment temperature is between 370-430 °C. At heat treatment of 430 °C, the elongation and the Brinell hardness of the alloy reached to 42.91% and 70.5 HB, respectively.

Abstract: The sectional observations of 13Cr-2Ni-2Mo and SUS 440C stainless steel ball bearings were done. Two features were found from the observations: parabolic-shaped cracks generated the flaking failure of 13Cr-2Ni-2Mo stainless steel bearing; jellyfish-shaped wear affected the flaking failure of SUS 440C stainless steel bearing.

Abstract: The interaction among cutting parameters during the turning process is complex and non-linear, hence making linear predicting methods unsuitable for use. This study is a presentation of hierarchical clustering of surface roughness using acoustic emission signals during single point diamond turning of RSA-443. The intention of the study is to establish if clusters generated by portioning algorithms can be reliably used to understand the internal structure of data. Acquisition of acoustic emission signals has been achieved by a Kistler Piezotron sensor. AE root mean square, prominent frequency and peak rate are extracted from the processed captured AE signals while surface roughness is physically measured using a Kistler Taylor Hobson Profilometer. Validation of the generated clusters has been achieved by using the Purity measure. The computed purity is 1, which is an exhibition of the high quality of the hierarchical clustering result. Hence, clustering can be reliably utilized to understand the internal structure of surface roughness data during single point diamond turning.

Abstract: When multicomponent molten pool nonequilibrium solidification, the interrelationship of location-dependent dendrite tip undercooling on low heat input and optimal growth crystallography is progressively discussed over planar interface morphology stability range to unidirectionally facilitate epitaxial growth by single-crystallinity control during laser repair of nickel-based superalloy to inhibit microstructure heterogeneity. Suppression of disoriented dendrite growth and crystallography orientation deviation along columnar interface is necessary for crackless repair. Axis-symmetrical (001)/[100] welding configuration kinetically reduces dendrite tip undercooling, nucleation and subsequent disoriented dendrite growth rather than unsymmetrical (001)/[110] welding configuration. When comparison between low heat input, within which laser power is limited and welding speed is rapid, and high heat input, within which laser power is considerable and welding speed is insignificant, the former attenuates dendrite tip undercooling and morphology transition between columnar and equiaxed dendrites to stabilize epitaxy and ameliorate dendrite growth with advantageous solidification conditions, especially drastic temperature gradient and small dendrite growth velocity. Axis-symmetrical growth crystallography and low heat input are favored to mitigate size of high-undercooling region, where stray grain formation are dominant, for homologous single-crystallization of epitaxial growth with satisfactory growth kinetics of dendrite tip, and are capable of elimination of undercooling-induced overgrowth for high quality weld, instead of aggressive unsymmetrical growth crystallography and high heat input. Additionally, the achievement of low heat input with axis-symmetrical welding configuration possesses stronger resistance to unstable interface morphology and solidification cracking. When comparison between growth regions of [100] and [010] crystalline orientation, where identical heat input is kept on both sides, wider dendrite tip undercooling is mainly located on the right side than left side to insidiously exacerbate crack-vulnerable dendrite growth, which is a ubiquitous phenomenon in the adverse (001)/[110] welding configuration. The effect of low heat input on dendrite tip undercooling is spontaneously smaller than growth crystallography. Hence, during nonequilibrium solidification of weld pool, the important mechanism of crystallography-induced microstructure heterogeneity obviation due to undercooling-limited epitaxial growth is consequently provided. The theoretical predictions cogently explain the experiment results in a concise way to properly illustrate microstructure degradation phenomena in the both sides of weld by reproducible calculation of mathematical modeling.

Abstract: In this study, the preparation method of the film-forming amine emulsion is explored by changing the sequence of different reagents, OLDA concentration, experimental temperature and OLDA/cyclohexylamine ratio. The stability of the film-forming amine emulsions prepared under different conditions is studied by observing if the emulsion delamination occurred after standing for several days. Results indicate that the sequence of different reagents, OLDA concentration, experimental temperature and OLDA/cyclohexylamine ratio affect the formation and stability of the film-forming amine emulsion obviously. The maximum content of OLDA in the film-forming amine emulsion could reach to 1.5 wt%, OLDA/cyclohexylamine ratio could be changed from 1:1 to 1:2.5, and room temperature could be as the experimental temperature. The stable film-forming amine emulsion could be prepared under the optimal conditions.

Abstract: Micro-arc oxidation (MAO) coating can significantly slow down the repaid degradation rate of biodegradable magnesium alloy, but the porous characteristics of the coating cannot provide long-term protection to magnesium alloy. In this paper, poly-lactic acid (PLA) was used to seal the porous MAO coating on the surface of extruded Mg-2Zn-0.5Zr-1.5Dy (mass%) magnesium alloy by a dipping coating method. Assessments were conducted by electrochemical experiment, immersion test, and hydrogen evolution experiment. The result shows that after the MAO-coated sample was dipped in PLA solution four times, the PLA could largely seal the porous and cracks of the MAO coating, and a dense MAO/PLA composite coating with a thickness of ~ 50 μm was prepared. The MAO/PLA composite coating provides good and stable protection to the alloy under 0~56 d immersion in the simulated body fluid than the single MAO coating, which shows an excellent application potential in the field of biodegradable magnesium alloy.

Abstract: The MCrAlY overlay coatings are widely used for high-temperature protection of hot section part of gas turbines and jet engines. This type of coatings are usually thermally sprayed using APS (Atmospheric Plasma Spraying), LPPS (Low Pressure Plasma Spraying) as well as HVOF (High Velocity Oxygen Fuel) methods. In present article the newly developed ethanol based HVOF gun was used for production of this type of coatings. The stainless steel 18-8 type was used as a base material. The AMDRY 386 (Oerlikon-Metco) NiCrAlY powder was used for coatings production. In the research different oxygen (400, 500, 600 NLPM) and ethanol (16.5, 18.3, 21.3, 23.6 and 26.6 dm³/h) flow ratio were selected for experimental processes. The powder feed ratio was also changed during process. After deposition the microstructural assessment using Scanning Electron Microscopy and chemical composition analysis using EDS method were conducted. The obtained results showed that coating was above 100 μm thick depending on the process parameters. The low concentration of pores and oxides was also observed on coatings cross-section. Using of ethanol HVOF gun enables to form good quality MCrAlY coatings with 50% reduction of oxygen consumption in comparison with conventional HP/HVOF torch using kerosene such as JP 5000. The other benefit of its using is lower CO₂ emission and lower concentration of carbon in coating in comparison with classic JP 5000 HVOF gun. The ethanol HVOF is a promising technology and might be considered as an replacement of LPPS and HVOF process for production of MCrAlY type of coatings.