Influence Of Solidification Conditions Research Articles

Influence of solidification conditions on chemical heterogeneities and dislocations patterning in additively manufactured 316L stainless steel

The dendritic substructure of 316L stainless steel processed by Laser Powder Bed Fusion (L-PBF) is experimentally investigated on three specimens built with significantly different scanning speeds and solidification cooling rates. Microstructural features of interest are misorientations between dendrites, gradients of chemical composition and dislocations structures. Similar amplitudes of chemical heterogeneities are found for all three samples, possibly related to the conjunction of relatively low variations of solidification rates and large partition coefficients for the considered solute elements. No crystalline misorientations between neighboring dendrites are observed, implying that interdendritic dislocations are not geometrically necessary dislocations stemming from solidification but arise from thermomechanical straining during post-solidification cooling. Dislocations patterning appear to be closely correlated to the periodicity of microsegregations, hinting at an effect of the local chemistry. No simple Hall-Petch-like effect of the dendrite size is observed on compression tests, possibly due to different strengthening mechanisms depending on the dislocations structures.

Influence of Solidification Conditions on the Microstructure of Laser-Surface-Melted Ductile Cast Iron.

The thermal conditions in the molten pool during the laser surface melting of ductile cast iron EN-GJS-700-2 were estimated by using infrared thermography and thermocouple measurements. The thermal data were then correlated with the microstructure of the melted zone. Additionally, the thermodynamic calculations of a Fe-C-Si alloy system were performed to predict the solidification path of the melted zone. It was found that increasing the cooling rate during solidification of the refined ledeburite eutectic but also suppressed the martensitic transformation. A continuous network of plate-like secondary cementite precipitates and nanometric spherical precipitates of tertiary cementite were observed in regions of primary and eutectic austenite. The solidification of the melted zone terminated with the Liquid → γ-Fe + Fe3C + Fe8Si2C reaction. The hardness of the melted zone was affected by both the fraction of the retained austenite and the morphology of the ledeburite eutectic.

Influence of solidification conditions and alloying elements Re and Ti on micropores formed during homogenization of Ni base single crystal superalloy

The influence of withdraw rate during directional solidification and elements Re and Ti on the formation of micropores during homogenization in Ni base single crystal superalloy CMSX-4 is investigated by X-ray tomography method. The results show that the number of micropores below 5 μm in sample solidified at 10 mm/min after homogenization at 1300 °C/3 h is greater than that in the case of 6 mm/min. The number of micropores below 10 μm in Re free and Ti free alloys is rather smaller than that of normal CMSX-4 alloy, while the number of micropores between 15 μm and 25 μm in Ti free alloy is relatively greater than that in Re free alloy. The variation of number of micropores is analyzed based on measurement of primary dendrite arm spacing (PDAS) and segregation ratios of alloying elements, the causes are mainly attributed to reverse segregation tendencies of Re and Ti and their remarkable diffusion coefficient difference, the increasing of PDAS also enhances the propensity of micropores formation during homogenization.

The Effects of Interfacial Heat Transfer Coefficient on the Microstructure of High-Pressure Die-Cast Magnesium Alloy AM60B

This paper describes the details of a quantitative experimental and numerical study on the influence of solidification conditions, including the apparent interfacial heat transfer coefficient (IHTC) between the die and solidifying metal, on the resulting local microstructure. Multiple runs of the commercial casting simulation package, ProCASTTM, are used to model the mold filling and solidification events employing a range of IHTC values. The simulation results are used to estimate the centreline cooling curve at various locations through the casting. The centreline cooling curve, together with the die temperature and the thermodynamic properties of the alloy are then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting. Finally, the local cooling rate is used to calculate the resulting grain size and skin thickness via previously established relationships. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent IHTC, which, in this study, was approximately 12000 W/m2·K. Additional useful observations from the numerical study suggest that the IHTC has a significant influence on the skin thickness and grain size in both the skin and core regions of the casting, while the effect of die temperature is limited to influencing the skin grain size only.

Influence of solidification conditions of billets of tin bronze BrO10C2N3 on its structure

Tin bronzes have found wide application in various branches of industry to fabricate parts operating under the friction conditions. For example, the distribution of the eutectoid component is regulated for bronze BrO10C2N3 when producing important parts. In this study, the influence of ingot casting and solidification conditions on the distribution and amount of eutectoid in the alloy structure is investigated. Several types of bronze casting into the water-cooled and uncooled mold, as well as when applying ultrasonic waves and without them, are tried out. These trials result in the development of casting tin bronze BrO10C2N3 into a combined casting mold situated in the ultrasonic field. The mold itself is a steel mold placed into a graphite filler with a heat-insulating insertion in the upper mold part. The results show that the application of a new technology make it possible to fabricate ingots in complete correspondence with requirements of the normative documentation and a high product yield over 70%.

Segregation of niobium in laser cladding Inconel 718 superalloy

Inconel 718 superalloy is widely used in the aerospace and turbine industry. Segregation of niobium appears in the laser cladding Inconel 718 superalloy and consequently influences the phase transformation during the rapid solidification. In order to control the microstructure and improve the mechanical properties of the deposited coating, the the influence of solidification conditions on the segregation of niobium and the resultant formation of Nb-rich Laves phase was studied using the microstructure observation and EDS analysis. The results show that the cooling rate has considerable influence on the microstructure of the deposited coating. High cooling rate is beneficial for suppressing the segregation of Nb and reducing the formation of Laves phase, which is believed to be detrimental to the performance of the Inconel 718 alloy.

Influence of solidification conditions on grain boundary cohesion in the mushy zone during directional solidification of nickel base superalloy

The effect of solidification rates on grain boundary (GB) cohesion in mushy zone during directional solidification was explored. The mushy zone structures were frozen by tin bath quenching. It was found that high solidification rate leads to an extended mushy zone thus vulnerable region, while there are larger areas where dendrites are bridged at higher solidification rate, i.e. there is a high fraction of bridging areas in the mushy zone as solidification rate is increased. The smaller hot tearing susceptibility at higher solidification rate cannot be explained by the greater mushy zone or vulnerable region, but it can be explained by stronger GB cohesion. The results suggest more attention should be paid to the GB cohesion rather than the range of mushy zone or vulnerable region in order to avoid hot tearing at least in some alloys.

Influence of solidification conditions on the castability of nickel-base superalloy IN792

The effect of withdrawal rate on hot tearing or solidification cracking during directional solidification (DS) was explored. High withdrawal rates were found to reduce the hot tearing tendency. There is a general refinement of the microstructure when the withdrawal rate is increased. First, the dendrite arm spacing appears smaller. Second, the columnar grain size is reduced. Third, the remaining liquid is finely dispersed and increasingly discontinuous. Finally, a more uniform distribution of strain is obtained because of the presence of more grain boundaries, and grain boundary cohesion becomes stronger due to the elimination of continuous liquid films. The reduced hot tearing susceptibility is attributed to the uniform distribution of strain and stronger grain boundary cohesion.

Influence of solidification conditions, thermomechanical processing, and alloying additions on the structure and properties of in situ composite Cu-Ag alloys

There is considerable interest in the development of high strength Cu-base composites with high conductivity for applications such as high field magnets, and essentially two alloy types have been examined, where a phase distributed in the Cu matrix during solidification is transformed into fine filaments during cold working of the material to sheet or wire. The present investigation was carried out to examine several poorly-understood aspects of processing, structure evolution, and strengthening in Cu-Ag alloys. The initial, as-solidified microstructure should play a role in determining the strength after working to sheet or wire, since it should influence the final microstructural scale. It is not known, however, to what extent the advantage of structural refinement by faster solidification may be usefully retained during working. The present study has examined the influence of Carbon and Zr mixed with the Cu-Ag alloy during melting in an attempt to reduce oxygen contamination and the ensuring possible embrittlement. At the same time, Zr may be expected to modify the kinetics and extent of age hardening in Cu-Ag solutions.

Influence of solidification conditions on γ′-phase thermal stability in 〈001〉 single crystals of Ni-based superalloys

Operating conditions for details of the nickel-based superalloys under long-term high-temperature loading necessitate high thermal stability of the alloy structure as a whole and {gamma}{prime}-phase especially, as the latter is an essential factor of the alloy strengthening. The direct investigation of the phase stability of superalloy specimens in the range of operating temperatures is of major interest. In the present work high-temperature X-ray technique was used to study the {gamma}{prime}-phase thermal stability upon heating in the temperature range from 20 C to 1200 C for a series of single crystal specimens of nickel-based superalloy ZhS 26 obtained using various regimes of the melt overheating before solidification.

Phase selection during laser surface melting of martensitic stainless tool steels

Laser surface melting (LSM) of tool steels allows for the complete dissolution of large brittle carbides, leading to homogeneous and extremely fine microstructures. Due to its characteristics, LSM allows improvement of the performance of tool steels by increasing their resistance to erosive and abrasive wear. Nevertheless, when DIN X42Cr13 and DIN X100Cr18 martensitic stainless steels are submitted to LSM, considerable amounts of austenite and {delta}-ferrite formed during the first stage of solidification can be retained in metastable condition at room temperature by mechanisms which are not yet fully understood. The purpose of the present work is to establish the influence of solidification conditions on the primary solidification mode of these two martensitic stainless tool steels, aimed to optimize the LSM operating conditions. Accordingly, samples of DIN X40Cr13 and DIN X100Cr18 were submitted to LSM with a wide range of solidification speeds. The microstructures were analyzed in order to identify the primary solidification mode. The experimental results were compared with theoretical predictions, based on comparison of the dendrite tip temperatures of austenite and {delta}-ferrite as function of the solidification speed.

すず鋳塊の湯じわ形成に及ぼす凝固条件の影響

すず鋳塊の湯じわ形成に及ぼす凝固条件の影響