Showing papers on "Liquation published in 2015"

Effect of heat treatment on the microstructure and mechanical properties of Inconel 718 processed by selective laser melting

Abstract: The microstructural and mechanical properties of Inconel 718 were determined on the specimens manufactured by selective laser melting (SLM) of prealloyed powder. High- density (99.8%) cylindrical specimens were built with four orientations (0°, 45°, 45°×45° and 90°) in relation to the building and scanning directions. Because of directional, dendritic-cellular grain growth, microstructure of the as-built specimens was characterized by columnar grains of supersaturated solid solution with internal microsegregation of Nb and Mo, demonstrated by fractions of Laves eutectic or its divorced form in interdendritic regions. Such a heterogeneous microstructure is unsuitable for direct post-process aging and makes the alloy sensitive to subsolidus liquation during rapid heating to the homogenizing temperature. In homogenized and aged condition, the alloy received a very good set of mechanical properties in comparison with the wrought material. In heat-treated condition, like in as-built condition, weak anisotropy of properties was found, manifested by lower Young's modulus, yield strength and tensile strength of the specimens extended along the build direction in comparison to the values for the other variants of the specimens. This is attributed to the fact that the grains maintained their geometric and crystallographic texture obtained during solidification.

Transgranular liquation cracking of grains in the semi-solid state

Abstract: Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ∼480 μm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism.

Liquation Cracking in Arc and Friction-Stir Welding of Mg-Zn Alloys

Abstract: As compared to Al alloys, which are known to be susceptible to liquation (i.e., liquid formation) and liquation-induced cracking, most Mg alloys have a lower eutectic temperature and thus are likely to be even more susceptible. The present study was conducted to study liquation and liquation cracking in Mg alloys during arc welding and friction-stir welding (FSW). Binary Mg-Zn alloys were selected as a model material in view of their very low eutectic temperature of 613 K (340 °C). Mg-Zn alloys with 2, 4, and 6 wt pct of Zn were cast and welded in the as-cast condition by both gas-tungsten arc welding (GTAW) and FSW. A simple test for liquation cracking was developed, which avoided interference by solidification cracking in the nearby fusion zone. Liquation and liquation cracking in GTAW were found to be in the decreasing order of Mg-6Zn, Mg-4Zn, and Mg-2Zn. Liquation cracking occurred in FSW of Mg-6Zn but not Mg-4Zn or Mg-2Zn. Instead of a continuous ribbon-like flash connected to the weld edge, small chips, and powder covered the weld surface of Mg-6Zn. The results from GTAW and FSW were discussed in light of the binary Mg-Zn phase diagram and the curves of temperature vs fraction solid during solidification.

Weldability studies on borated stainless steel using Varestraint and Gleeble tests

Abstract: Borated austenitic stainless steels are widely used in nuclear applications due to their higher neutron absorption efficiency. Weldability of these steels is a major concern due to the formation of low-melting eutectics enriched in iron, chromium, molybdenum and boron. Varestraint and Gleeble-based tests have been carried out to evaluate the solidification and liquation cracking behaviour of 304B4 Grade B stainless steel. The solidus and liquidus temperatures have been determined using differential scanning calorimetry and Scheil simulation for solidification of welds. The results indicate that this steel has good solidification cracking resistance due to the backfilling effects of eutectic borides. However, liquation cracking resistance in this steel is moderate due to its wide nil ductility range. This paper discusses the role of boron on hot cracking susceptibility of this borated austenitic stainless steel using both the Varestraint and Gleeble-based hot ductility tests.

Microstructural characterisation and liquation behaviour of laser welded joint of fine grained AZ91 magnesium alloy thin sheets

Abstract: Fine grained AZ91 sheets of 1 mm in thickness were successfully welded by autogenous laser beam welding and laser beam welding with filler strip. Both welded joints are characterised by fine equiaxed dendrites in the fusion zones and free from significant grain coarsening in the heat affected zones. There are two kinds of liquation reactions in the partially melted zone of the autogenous laser beam welding joint, which are associated with the melting of residual bulky β-Mg17Al12 phase and the constitutional liquation of submicrometre β-Mg17Al12 precipitates. No liquation reaction is detected in the welded joint obtained by laser beam welding with filler strip. The laser beam welding joint with filler strip for AZ91 thin sheets is free from evident collapse.

Nonmetallic Inclusions and Promising Principles for Improving the Set of Properties and Quality Characteristics of Steel

Abstract: Results of a detailed study of continuously-cast low-alloy pipe steel metal demonstrate a significant difference in micro- and macrostructural states, including the presence and extent of equiaxed and columnar crystal areas in relation to the later stages of ladle treatment A marked difference is also recorded in impact strength indices, hydrogen corrosion cracking resistance, and other service properties obtained for different rolled billets It is established that as a result of adding large amounts of silicon- and manganese-containing ferroalloys in the later stages of ladle treatment or in the process of steel continuous casting there is formation of liquid silicate inclusions Due to a high silica content during steel crystallization these inclusions are converted into a supercooled liquid or glassy condition and acquire irregular shape, filling the space between growing crystals As a result of this they effectively reduce the intensity of mass- and heat-transfer during steel crystallization, block development of liquation processes, and facilitate an increase in the degree of metal structural and chemical inhomogeneity As a consequence there is an increase by a factor of 2–25 in impact strength to extremely high values (KCV–40 more than 400–420 J/cm2), and rolled product hydrogen cracking resistance

Direct Observation of Liquation in Ni-Base Superalloy by Using Confocal Laser Scanning Microscopy

Abstract: In-Situ direct observation was used to observe the liquation in an Inconel 617. High-Temperature Confocal Laser Scanning Microscopy (HT-CLSM) was used to observe the phenomena. Experiment was perform at 1330 °C with heating rate 5 °C/s. Results showed that the liquidation started at 1319.2 °C (268.08 seconds) in which liquid formed around precipitate. At 1330.5 °C (272.05 seconds) the liquid film wet and penetrated along grain boundaries. Then after 277.05 seconds, sufficient liquid film formed and moved freely on the surface of the specimen across grain boundaries. After cooling to room temperature, the test specimen was analyzed for local chemical composition gradient of precipitates and liquid film. Precipitate morphology changed from polygonal shape to round shape using SEM and EPMA. The results from this observation could be used to explain liquation mechanism occurred in Inconel 617 during heating.

Ferronickel-based alloy welding joint heat-affected zone grain boundary liquation crack control method

Abstract: The invention relates to the field of ferronickel-based alloy welding, particularly to a ferronickel-based precipitation strengthening austenite alloy (J75) joint heat-affected zone grain boundary liquation crack control method. The method solves the problem ferronickel-based alloy joints are prone to forming relatively wide gamma'-depleted zones or grain boundary liquation cracks. The ferronickel-based alloy welding, particularly to a ferronickel-based precipitation strengthening austenite alloy joint heat-affected zone grain boundary liquation crack control method is implemented through vacuum electron beam welding and composed of the technological processes of pre-welding base metal treatment, vacuum welding chamber internal clamping and fixing, welding chamber vacuumizing, positioned welding, single-cycle welding with electron beam deflective scanning, post-welding modification welding and post-welding electron beam defocused welding joint scanning. Ferronickel-based alloy joints welded through the method have no gamma'-depleted zones and grain boundary liquation cracks on the heat-affected zones, are good in surface forming and achieve a joint strength higher than 980 MPa or even 1030 MPa, a strength coefficient of base metal higher than 0.9 and an impact toughness (akU) higher than 980 KJ/m2 or even higher than 1020KJ/m2.

Tin smelting liquation furnace

Abstract: The invention relates to the field of mineral smelting equipment and discloses a tin smelting liquation furnace. The tin smelting liquation furnace comprises a furnace bottom, a furnace body and a furnace top, wherein the furnace body is surrounded by four furnace walls, the furnace bottom is a high-aluminum brick pavement layer, the furnace walls and the furnace top are constructed by refractory bricks, and a top feed opening is formed in the furnace top; a tin discharge opening is formed at the bottom of the tail end of the furnace body, a refractory brick layer is built on the surface of the furnace bottom, three surfaces of the refractory brick layer are high, one surface of the refractory brick layer is low, and the refractory brick layer inclines towards the direction of the tin discharge opening; a ventilating furnace door is arranged on the furnace wall, a fuel inlet is formed in the front end of the furnace body, a smoke outlet on the tail end of the furnace body is connected with an exhaust fan, and the exhaust fan pumps air from inside to outside to generate a negative pressure in the furnace body. By adopting the tin smelting liquation furnace provided by the invention, the problems of non-uniform temperature, feed difficulty and the like of the existing liquation equipment are solved, and the tin smelting liquation furnace has the characteristics of convenience in feeding, simple temperature control and the like.

Microstructure of surface layer of T1 and D2 steels after laser melting

Abstract: The aim of this study was to investigate the in-depth structure transformations of the laser-melted layers of the steels mostly used in tool production – T1 and D2 steels. The experiments of laser surface melting of T1 and D2 steels were done with continuous wave CO2 laser (wavelength λ = 10.6 μm). The sample’s microstructure was investigated, and the EDX analysis was made by SEM JEOL JMS-35C. Our results show that the microstructural changes of the laser-melted layer of T1 steel were determined by the process of directed crystallisation from the bottom layer to the surface. There is considerable inhomogeneity, followed by the predominantly ongoing process of chemical liquation during crystallisation. Cellular structure, consisting high-carbon martensite and significant amount of retained austenite, prevails in the melted pool bottom. Austenite–carbide eutectic with possible presence of lamellar martensite is situated along the dendrites’ boundaries (in inter-dendrite spaces). The austenite–carbid...

Hot Ductility Loss in a Fe-Ni-Based Superalloy

Abstract: High temperature tensile tests have been conducted on samples of a Fe-Ni based superalloy, Incoloy A-286, and significant ductility loss has been observed at 1220 °C. Titanium-rich, thin-film-like phase has been found on the inter-granular facets of fracture surfaces. It appears that sulfur content of Ti-rich phase was higher than that of the matrix. At 1220 °C, liquation of Ti-rich phases has resulted in thin-film-like morphology along the grain boundary and caused the ductility loss during tensile deformation.

Special features of the formation of the microstructure and chemical heterogeneity in welded joints in alloys of the Al–Zn–Mg–Cu system alloyed with scandium

Abstract: Special features of the formation of the microstructure and the development of chemical heterogeneity in the weld metal and heat-affected zone (HAZ) in arc welding of a complex alloyed alloy of the Al–Zn–Mg–Cu system are discussed. It is shown that the effect of welding heating results in melting of the phase components of the alloy in the HAZ with the formation of structures of the eutectic origin in the form of long interlayers at the boundaries of recrystallized grains, causing brittleness of the metal. Alloying the alloy with scandium reduces the intensity of the processes of recrystallization and the extent of liquation at the grain boundaries and also localizes the melting of the grains without the formation of thick eutectic interlayers.

Structural heredity of alloys produced by centrifugal SHS: Influence of remelting temperature

Abstract: NiAl-based high alloy doped with boron was produced by centrifugal SHS and then subjected to remelting at several remelting temperatures (Trm) above its melting point (Tm = 1640°C) in order to elucidate the influence of Trm on structural heredity of the synthesized alloy. Induction remelting in vacuum at Trm > Tm + 100°C was found to markedly enlarge the size of structural constituents and lead to liquation. The remelting at 1740°C did not result in formation of new phases; it gave rise only to some redistribution of structural constituents The synthesized allow comprised a matrix of NiAl-based solid substitutional solution with embedded reticular inclusions of Ni20Al3B6 and lamellar (Mo,Cr)B precipitate.

Heating device for be used for producing basalt continuous fibers

Abstract: The utility model discloses a heating device for be used for producing basalt continuous fibers, including fuel line and suit in the inside combustion-supporting trachea of fuel line, the top of fuel line with the outer wall sealing connection of combustion-supporting trachea, the suit is gone back to the outside of fuel line has and is used for the cooling protection the fuel line with combustion-supporting tracheal condenser tube, condenser tube's top with the outer wall sealing connection of fuel line, the condenser tube top is provided with water inlet and delivery port. The device can make fuel and combustion-supporting gas burn in the basalt liquation effectively, and the heat of production directly transmits gives the basalt liquation, and combustion product becomes bubble stirring basalt liquation simultaneously to having improved the melting rate of basalt building stones, having makeed basalt liquation temperature and composition more even, the large-scale industry metaplasia that more is favorable to realizing basalt continuous fibers is produced.

On the problem of liquation of alloying elements in the structure of single-phase austenitic steel

Abstract: The results of study on the chemical composition of austenitic steel for 12 elements in standard parts, obtained by casting, and used for critical parts of machines and mechanisms at elevated temperatures of operation, are discussed. Anomalous segregation of some elements set the practical limits of the instability of the chemical composition of austenitic cast steel structure.

Revolve cylinder forced air cooling casting machine

Abstract: The utility model relates to a revolve cylinder forced air cooling casting machine relates to metallurgy, smelts liquation casting technical field. As follows mainly organism (5), revolve a section of thick bamboo (4), a multi -screw (4 -3), remove and water car (2) and constitute. Its purpose is the cylinder that utilizes several layers of rotation and revolve the multi -screw on the section of thick bamboo, cuts apart into the granule of settlement volume with the liquation, is revolving during a section of thick bamboo rotates, makes the liquation roll along the helix, and the liquation solidifies shapingly in the roll, and air -cooled air current is in succession along the helix input, makes the successive cooling that receives air -cooled air current of the rolling surface of liquation or high temperature granule. Realizing smelting the casting of liquation granule simultaneously, improving casting particle surface density. A material loss strengthens anti differentiation ability that is used for the ferroalloy product to take shape, can eliminate and caused by the hand breaking . an increase productivity that the casting that is used for metal, non ferrous metal dysmorphism spindle, breed the piece can be high.

Study of the effect of liquation on structure and durability of intermetallic alloys based on nickel

Abstract: The effect of liquation heterogeneity on structure and phase composition of the VIN intermetallic alloys (VIAM, intermetallic nickel alloy) and the regimes of heat treatment of the intermetallic alloy are studied. The effect of liquation heterogeneity on durability of the intermetallic alloy at high temperature is analyzed.

Method for purifying industrial silicon by synchronously electroslag remelting and alloy liquation refining

Abstract: The invention relates to an impurity removal method belonging to the field of alloy materials, particularly a method for purifying industrial silicon by synchronously electroslag remelting and alloy liquation refining. The method mainly comprises the following steps: (1) premelting industrial silicon and a metal liquation agent into an alloy, and making a consumable alloy electrode; (2) in an electroslag furnace, melting a slag melting agent into a slag basin by using an arc starting agent, overheating the slag basin, and immersing the consumable alloy electrode into the slag basin to perform electroslag remelting refining and alloy segregation refining; and (3) after finishing the refining and solidifying, obtaining a segregation alloy cast ingot, crushing and separating to obtain the purified polycrystalline silicon. Compared with the traditional metallurgical process, the method has the advantages of obviously higher impurity removal efficiency, short process and simple equipment, and is convenient to operate; and the refined material has the advantages of higher purity, fewer impurities, and uniform and compact chemical component and structure. In the electroslag remelting process, liquid slag protection always exists, thereby preventing the liquid alloy from directly contacting air, and preventing the oxidation loss of the silicon and metal liquation agent.