Molten Pool Temperature Field Research Articles

Microstructure evolution, mechanical properties of FeCrNiMnAl high entropy alloy coatings fabricated by laser cladding

In this work, FeCrNiMnAl high entropy alloy (HEA) coatings under different laser energy density (Led, 50–92 J/mm2) were fabricated on 17-4PH stainless steel by laser cladding (LC). The influence of different laser energy density on the geometric morphology, microstructure, microhardness and tribological properties of HEA coating was investigated. To obtain the specific solidification parameters (temperature gradient and solidification rate), the finite element model was established to express the transient change of molten pool temperature field. The columnar-to-equiaxed transition (CET) corresponding to different zones of HEA coating was revealed. The result showed that the geometric parameters increased with the rise of Led because of the Marangoni convection. Equiaxed crystals and columnar crystals were distributed on the top and bottom zones of HEA coatings respectively, and the CET behavior was observed. Higher temperature gradient and lower solidification rate were conducive to the growth of columnar-crystals. Furthermore, at the Led of 92 J/mm2, HEA coatings showed relatively high crack sensitivity. HEA coatings significantly improved the tribological properties owing to metal oxide particles generated by oxidation. In the mechanical properties test, the maximum microhardness of prepared HEA coating (1800 W) was 587.83 HV0.2, which was 1.63 times that of 17–4PH substrate. Metal oxide particles generated a flat wear-resistant enamel layer which protected the coating surface. The tribological properties was optimal at the Led of 64 J/mm2, the average friction coefficient and wear rate were 0.4654 and 7.026 × 10−8 mm2/N, respectively.

Multi-scale simulation of columnar-to-equiaxed transition during laser selective melting of rare earth magnesium alloy

• A model for studying the columnar-to-equiaxed transition during selective laser melting of rare earth magnesium alloy is developed. • The liquid undercooled layer under the combined action of forced cooling, the temperature gradient and the liquid solute concentration gradient leads to columnar-to-equiaxed transition. • The effects of Zr solubility in magnesium matrix and preheating temperature on columnar-to-equiaxed transition are obtained. A model of coupling macro finite volume method (FVM) and cellular automata (CA) is proposed in this paper to explore the columnar-to-equiaxed transition (CET) during selective laser melting (SLM) of rare earth magnesium alloy. Taking into account the impact of recoil pressure and Marangoni convection on the molten pool temperature field, the grain structure is simulated. As suggested by the simulation results, with the undissolved Zr serving as heterogeneous nucleation sites, the liquid undercooled layer under the combined action of forced cooling, the temperature gradient and the liquid solute concentration gradient leads to CET. While considering the dissolution of Zr in magnesium matrix, the results demonstrate that the dissolution of element Zr is effective in significantly inhibiting the growth of columnar crystals and ensuring the sufficient constitutional supercooling (CS) required for nucleation. In addition, to raise the preheating temperature contributes to enhancing the outcome of nucleation and incresing the grain size. Invoking the interdependence model (IM), with the cooling rate gradually increasing in the SLM process of magnesium alloy, the nucleation-free zone (NFZ) reduces by decreasing the solute diffusion layer in the front of the solid/liquid (SL) interface and the temperature gradient. The reduction in temperature gradient can promote undercooling for nucleation and facilitate the development of equiaxed crystals. The simulation results are qualitatively verified as highly consistent through experimentation.

Study on the Molten Pool Fluid Behavior of PAW-Cable-Type Seven-Wire GMAW Hybrid Welding

Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of the molten pool temperature field and flow field and experimental verification were conducted on Q235 thin plate hybrid welding with cable-type wire to explore molten pool fluid behavior. The simulation results show that keyholes form in the molten pool due to the strong penetration ability of a plasma arc and then the evolved pores by the surface tension float out of the molten pool. When the GMAW welding current increases, both the length and width of the weld pool enlarge, the weld reinforcement increases and the flow rate of molten metal in the weld pool also speeds up. While the PAW current increases, the weld pool length also increases and the molten metal in the weld pool significantly flows faster, but the weld reinforcement decreases. When the welding speed increases, the weld pool length and fusion depth decrease, but the reinforcement will first increase and then decrease. The experimental results are in strong agreement with the simulation results. It shows that the numerical analysis model established in this paper is accurate, laying a certain theoretical foundation for the popularization of PAW-cable-type seven-wire GMAW hybrid welding.

Characteristics of the Molten Pool Temperature Field and Its Influence on the Preparation of a Composite Coating on a Ti6Al4V Alloy in the Micro-Arc Oxidation Process.

In this study, the phase transition of secondary phase particles in a composite coating is used to estimate the temperature field of the molten pool on a Ti6Al4V alloy in the micro-arc oxidation (MAO) process. The behavior of the sparks and the molten pool during the MAO process was observed in real-time by a long-distance microscope. The microstructures and compositions of the composite coatings were studied by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results revealed that, for the temperature field distribution range of the molten pool in the active period, the lower limit is 2123 K and the upper limit is not lower than 3683 K. The reason for the multiphase coexistence is that the high-temperature phase is retained by the rapid cooling effect of the electrolyte, and the low-temperature phase is formed due to secondary phase transformation during the long active time of the molten pool temperature field. The strengthening mechanism of the composite coating prepared by adding the secondary phase particles is elemental doping rather than particle enhancement. The secondary phase particles are able to enter the composite coating by adhering to the surface during the cooling process. The secondary phase particles will then be wrapped into the coating in the next active period.

Hump weld bead monitoring based on transient temperature field of molten pool

The molten pool images of GMAW (Gas Metal-Arc Welding) was acquired during the base time period using a self-built system for measuring the transient temperature field of molten pool. The transient temperature field of the molten pool of GMAW at different welding speeds was calculated based on the principle of colorimetric temperature measurement. When analyzing the temperature distribution at the middle and tail region of the molten pool in the process of hump bead formation under high speed GMAW, it was found that the temperature distribution of the molten pool is uneven perpendicular to the welding direction, and this law does not accord with the time when the hump appears in the image, and the accuracy rate accorded with the law was also counted. Through this rule, the welding robot can adjust and control the process in time before the appearance of hump, and the prediction of hump before bead formation under GMAW is preliminarily realized.

Ti6Al4V激光熔化沉积熔池温度场与微观组织特性

Ti₆Al₄V激光熔化沉积熔池温度场与微观组织特性

Microstructures in Solidification Simulation of Electron Beam Scanning with MC in Molten Pool

The solidification microstructure of electron beam scanning is important to product performance. The solidification process of molten pool temperature field and 2D simulation mathematical model of grain growth was established based on heat transfer and the physics of growth process of crystal grains. The heat distribution, thermal physical parameters and influence of thermal radiation on the temperature field was considered during the analysis process. The distribution of temperature field was solved by COMSOL. The process of solidification was simulated by using Monte Carlo method. Using optical microscope to observe the solidified microstructure of bath. The simulation results show that the mathematical model can reasonably describe the grain growth process, the temperature field and the simulation of microstructure morphology.

Temperature Field Numerical Simulation of Screwy Thin-Walled Part Cladded by Hollow Laser Beam

A numerical simulation model of laser cladding based on internal powder feeding through a hollow laser beam is set up by the Ansys Parametric Design Language (APDL). Through analyzing this model, the saddle-shaped distribution of energy absorbed in scanning direction is found and the molten pool temperature field of single laser cladding is observed like a comet[. Base on the single laser cladding experiments, the initial parameters and test plans of laser cladding and the screwy thin-walled part forming are confirmed. The finite element model of laser cladding forming screwy thin-walled part is established. The evolution of temperature field and thermal cycle of the nodes are studied during the screwy thin-walled part forming process. In the emulation laser power is controlled real time according to the analyses above, and the changing value of laser power is obtained to keep the molten pool temperature steady. The screwy thin-walled part is formed successfully based on these data.

Numerical Simulation of Three-Dimensional Molten Pool Temperature Field and Flow Field for Laser Melt Injection Based on Fluent

According to the characteristics of laser melt injection, a numerical model for a simplified 3D transient temperature field in molten pool was established using FLUENT software in this paper. In the model, many factors were considered such as liquid metal turbulence, latent heat of phase transformation and material thermo physical properties depending on temperature. The results show that the model can be developed well by FLUENT software. And the results also show that the driving force of the liquid metal flow mechanism.

Numerical Simulation for Shaping Feature of Molten Pool in Twin-Arc Submerged Arc Welding

The notion of ratio of width to length is proposed to describe the shaping feature of molten pool of twin-Arc submerged arc welding accurately, and analyze the law of molten pool variation and weld formation. The temperature field finite element numerical simulation model of twin arc movement is established. The loading form of twin-arc with double ellipsoid heat source is discussed. The molten pool temperature field of twin-arc submerged arc welding is calculated and analyzed under different process parameters. The law of molten pool characteristics influenced by the welding speed, current and voltage of twin-arc submerged arc welding parameters is analyzed. The relation between shaping feature of molten pool and weld formation is discussed according to the ratio of width to length. The results manifested that the width to length ratio of weld pool decreases with the improvement of welding speed, which result in gene- ration of weld defects. The width to length ratio of weld pool is increased by adjusting the proportion of the current, voltage and the distance of the two arcs, which avoids the generation of weld defects.

Special Software for Laser Molten Pool Temperature Field Based on LabVIEW

Special software for laser molten pool temperature field based on LabVIEW was developed．Thermal radiation image of laser molten pool temperature taken by CCD were processed by the special software. It was shown that the software had a visual interface and the laser molten pool temperature field could be measured at real-time and the whole system is simple and efficiency. The software is easy to operate and can measure the laser molten pool temperature field quickly and exactly.

Measurement of Temperature Field in Laser Molten Pool by CCD Based on DSP

In this paper, a measurement system of temperature field in laser molten pool by CCD based on DSP is presented. The paper also presents the system of hardware, software process, and the method of image processing by DSP. To solve the real time problem in the processing of measuring the temperature field, the system uses DSP as the main CPU, processing the image without a computer. By this method, the system can become simple and efficient and measure the laser molten pool temperature field quickly and exactly. Gradient image of temperature field is displayed on LCD after real time processing by this system. The final picture of temperature field can be directly analyzed.

氧碘化学激光辐照纯铝的温度场数值模拟

氧碘化学激光辐照纯铝的温度场数值模拟

溶融池温度場に及ぼす硫黄含有量の影響―紫外線放射測温法の開発（第２報）―

The alloying element in steel, such as sulfur has been of great concern in welding, because sulfur is an element that significantly changes the weld penetration. To analyze the minor element effect experimentally, accurate information on the molten pool, such as temperature or fluid flow, is essential. The radiation thermometer is commonly used to obtain the temperature field of the object. However, the emissivity problem occurs in measuring temperature of molten metals. The emissivity fluctuation causes a noticeable error in temperature indicated by radiation thermometers. As described in the previous paper, the UV (ultra-violet) radiation thermometer is useful to solve the emissivity problem.In the present paper, the influence of sulfur content on temperature field of molten pool is discussed. In order to avoid interference from arc plasma, the measurement was carried out from the bottom side. It was found that temperature distribution was asymmetrical, and changes in sulfur content can change molten pool formation. As a result, it was made clear that changes in sulfur content also affected temperature field of molten pool.