Eutectic Precipitation Research Articles

Significantly Promoting the Thermal Conductivity and Machinability of Negative Thermal Expansion Alloy via In Situ Precipitation of Copper Networks.

Rapid advancements in electronic devices yield an urgent demand for high-performance electronic packaging materials with high thermal conductivity, low thermal expansion, and great mechanical properties. However, it is a great challenge for current design philosophies to fulfill all the requirements simultaneously. Here, an effective strategy is proposed for significantly promoting the thermal conductivity and machinability of negative thermal expansion alloy (Zr,Nb)Fe2 through eutectic precipitation of copper networks. The eutectic dual-phase alloy exhibits an isotropic chips-matched thermal expansion coefficient and a thermal conductivity enhancement exceeding 200% compared with (Zr,Nb)Fe2, along with an ultimate compressive strength of 550MPa. The addition of copper reorganizes the composition of (Zr,Nb)Fe2, which smooths the magnetic transition and shifts it toward higher temperature, resulting in linear low thermal expansion in a wide temperature range. The highly fine eutectic copper lamellae construct high thermal conductivity networks within (Zr,Nb)Fe2, serving as highways for heat transfer electrons and phonons. The in situ forming of eutectic copper lamellae also facilitates the mechanical properties by enhancing interfacial bonding and bearing additional stress after yielding of (Zr,Nb)Fe2. This work provides a novel strategy for promoting thermal conductivity and mechanical properties of negative thermal expansion alloys via eutectic precipitation of copper networks.

Eutectic Precipitate Dissolution and Microstructure Evolution of Cr–W–Co Heat-Resistant Steel with Varying Ce Contents

Eutectic Precipitate Dissolution and Microstructure Evolution of Cr–W–Co Heat-Resistant Steel with Varying Ce Contents

In Situ High-Pressure Correlated Transportation of Heavy Rare-Earth Perovskite Nickelates as Batch Synthesized within Eutectic Molten Salts at MPa-pO2.

The multiple magneto-/electrical quantum transitions discovered with d-band correlated metastable perovskite oxides, such as rare-earth nickelate (ReNiO3), enable applications in artificial intelligence and multifunctional sensors. Nevertheless, to date such investigation merely focuses on ReNiO3 with light or middle rare-earth composition, while the analogous explorations toward heavy rare-earth (ReHNiO3, ReH after Gd) are impeded by their ineffective material synthesis relying on GPa pressure. Herein, for the first time we synthesized the powder of ReHNiO3 in grams/batch with ∼1000 times lower pressure and ∼300 °C lower temperature in comparison to the previous ∼101 milligram/batch results, assisted by their eutectic precipitation and heterogeneous growth within alkali-metal halide molten salt at MPa oxygen pressures. Further in situ characterizations under high pressures within a diamond anvil cell reveal a distinguishing pressure predominated bad metal transport within the nonequilibrium state of ReHNiO3 showing high-pressure sensitivity up to 10 GPa, and the temperature dependences in electrical transportations are effectively frozen.

Precipitate Dissolution and Grain Growth during Solution Treatment of Ce‐Containing 15Cr–22Ni–1Nb Austenitic Heat‐Resistant Steel

The precipitate dissolution and grain growth during the solution treatment of a newly developed Ce‐containing 15Cr–22Ni–1Nb steel are investigated. The dissolution of eutectic NbC is the result of the elements diffusion along the concentration gradients, and honeycomb (Fe,Cr,Ni,Si)2(Nb,Mo) Laves phase transforms into a more stable Mo2C‐type M2C carbide. As the cerium content is increased from 0 to 0.0630 mass%, the area fraction of eutectic precipitates in forged and solution‐treated 15Cr–22Ni steel is decreased first and then increased. For the steel with 0.0055 mass% cerium content, the substantial reduction in the area fraction of precipitates during hot forging and solution treatment is ascribed to the severe abnormal grain growth. In the case of 15Cr–22Ni steel with 0.0019 and 0.0630 mass% cerium content, the average size of austenite grains after solution treatment is reduced, the multipeak development of grain size distribution is restrained, the range of grain size distribution is narrowed, and the variation coefficient of grain growth, the critical size of abnormally grown grain, and the proportion of abnormally grown grain are all decreased. The variation coefficient of grain growth and the critical size of abnormally grown grain in the steel are increased as the solution time is extended, whereas the proportion of abnormally grown grain presents a general trend of reduction. The established mathematical model of grain growth in the paper can be well applied to predict and control the average size of austenite grains in 15Cr–22Ni steel after solution treatment.

Investigation on creep behaviours of centrifugal casting 27Cr44Ni5W3Al+MA alloy used as ethylene pyrolysis furnace tube at 1050°C

ABSTRACT For centrifugal casting 27Cr44Ni5W3Al+MA alloy used in ethylene pyrolysis furnace, its creep behaviours at 1050°C are investigated. The results show that the alloy undergoes three stages during the creep tests under different stress levels ranging from 18 MPa to 30 MPa. The apparent stress index n of the alloy is 6.11, and the creep deformation mechanism is mainly dislocation climbing. During the creep test, the fishbone-like M7C3 inside eutectic precipitates in casted alloy gradually transform to massive M23C6 at the edge of the precipitate. Creep induced voids germinate and connect at the interface of austenite/M23C6 and austenite/Ni3Al, the cavities expand along the M23C6 and Ni3Al, forming micro-cracks and the alloy eventually cracks.

Microstructure and wear behaviors of a WC10%-Ni60AA cermet coating synthesized by laser-directed energy deposition

This study successfully prepared crack-free WC10%-Ni60AA cermet coatings with high hardness using directed-energy deposition incorporating substrate preheating up to 500 °C. At the bottom of the deposit, the crack-free coating microstructure exhibited a lamination layer with a coarse herringbone eutectic, and the crystal-microstructure phase mainly comprised γ-Ni solid solution and eutectic precipitation Ni17W3, Ni31Si12, and Cr23C6. At the middle and top of the deposit, the microstructure exhibited a dense net-like eutectic, including a dendritic with the main phase of γ-Ni solid solution, interdendritic with a main phase of Cr23C6, and subdendritic with a main phase of Ni31Si12, Ni17W3, and a small block-like precipitate with a main phase of Cr2.4W0.6Si. Furthermore, the deposits on the substrate preheated to 500 °C exhibited the highest hardness (812 HV, an increase of 64 % compared to that of the non-preheating sample) owing to the dense net-like eutectic precipitation with fine-grain structure. Furthermore, wear test results show that the wearing process is divided into three stages: the rapid-increase stage; the plowing-friction stage; and the stable-wear stage. Specifically, as the load increased from 100 N to 400 N, the width and depth of the wear tracks increased, and the wear mechanisms were adhesive and oxidation, with the most severe wear occurring under a load of 400 N. Similarly, as the speed increased from 50 RPM to 300 RPM, the width and depth of the wear tracks increased, and the wear mechanisms were adhesive and oxidation at low speeds. When the speed was increased to 300 RPM, the most severe wear occurred, and the wear mechanisms were primarily adhesive and abrasive, along with a small amount of oxidation wear.

A study of crystallization kinetics, phase formation and magnetic properties of (FeCoNiMn0.25Al0.25)75Si13B12 high-entropy metallic glass

The crystallization kinetics, phase formation and magnetic properties of (FeCoNiMn0.25Al0.25)75Si13B12 high-entropy metallic glass are investigated by thermal analysis, electron microscopic imaging, X-ray and magnetic tests. The results indicate that the alloy combines good glass forming ability and thermal stability. After heat treatment, the alloy precipitates with a feature of three-dimensional growth, while the α-Fe,Co phase first precipitates, and following the lamellar eutectic precipitate as Fe-B and Co2Si. This ultra-fine α-Fe,Co at low temperatures and the solid solution of non-ferromagnetic elements in the α-Fe,Co at high temperatures decrease the saturation magnetization of the alloy. In addition, the change from antiferromagnetic to ferromagnetic of Mn is confirmed through first-principles density functional theory calculations.

Effect of Homogenization Treatment on Microstructure and Eutectic Precipitates in Ce‐Containing 15Cr–22Ni–1Nb Austenitic Heat‐Resistant Stainless Steel

The effects of homogenization temperature and time on microstructure and eutectic precipitates in Ce‐containing heat‐resistant stainless steel are studied. The increase in the homogenization temperature and time promotes the diffusion of alloying elements and the transition from dendrite structure to austenitic grain. Laves phase particles are fully dissolved after the homogenization of the ingots regardless of the cerium contents and homogenization temperature and time, except for the case of the homogenization at 1130 °C for 4 h. Honeycomb Laves phases gradually dissolve and become clusters of small blocky during homogenization treatment. The amount of eutectic NbC dissolved into the matrix is increased with the increase in the homogenization temperature and time. The solubility of niobium and carbon in austenite is increased with increasing the cerium content, which is beneficial to the dissolution of eutectic NbC. The distribution homogeneity of alloying elements in the austenitic matrix is increased with the increase in the cerium content. The homogenization temperature for reaching full diffusion of alloying elements into austenitic matrix is decreased with increasing the homogenization time. The decrease in the secondary dendrite arm spacing by cerium addition is favorable to the homogenization of alloying elements during homogenization treatment.

Microstructure evolution and mechanical properties strengthening in laser powder bed fusion of high-strength SiC and TiB2 co-reinforced Al-Zn-Mg-Cu composites

A SiC and TiB2 particles reinforced Al-Zn-Mg-Cu matrix composite was designed and fabricated using laser powder bed fusion (LPBF). This study investigated the effects of ceramic reinforcements on the phase composition, microstructures, grain crystallization, and mechanical properties. The mechanisms of microstructure evolution and mechanical strengthening were discussed. Results show that a multi-level microstructure with ceramic reinforcements and nanoprecipitates has been developed. The ceramic reinforcements exhibited a uniform distribution within the matrix, while the eutectic precipitates formed a network substructure along the grain boundaries. A novel interfacial bonding mechanism, SiC/Al4C3 +eutectics/Al, has been developed through an in-situ reaction between SiC and Al. Ceramic reinforcements provided sufficient nucleation sites for grain nucleation, transforming from coarse columnar growing along the [001] direction parallel to the printing direction to fined equiaxed grains with random growth. The mechanical properties were enhanced, and the microhardness heterogeneity along different directions was reduced. The ultimate tensile strength and elongation were 516 ± 12 MPa and 6.12 ± 0.36%, respectively. The enhancement of mechanical properties was attributed to superior interfacial bonding strength, fine grain strengthening, solution strengthening, second phase strengthening, and substructural strengthening. This work could demonstrate the potential for fabricating AMCs using LPBF with Al-Zn-Mg-Cu alloy as the matrix.

Solidification Characteristics and Eutectic Precipitates in 15Cr–22Ni–1Nb Austenitic Heat-Resistant Stainless Steel

Solidification Characteristics and Eutectic Precipitates in 15Cr–22Ni–1Nb Austenitic Heat-Resistant Stainless Steel

Plasma electrolytic oxidation of as-cast and heat-treated binary Al-Ni alloys

In this study, the effect of nickel addition on the plasma electrolytic oxidation (PEO) behavior of pure Al was investigated. Binary Al-Ni alloys containing 1, 3, 5 and 7 at. % Ni were produced by two step vacuum arc and induction melting methods. Produced alloys and pure Al as a reference were PEO coated in a silicate-based alkaline electrolyte through a bipolar power source under constant voltage mode for 45 min. The samples were characterized by XRD, SEM-EDS and Vickers microhardness tester before and after PEO. All alloys were consisted of Al and Al3Ni phases. Fine rod-like eutectic structure was evident for 1 (hypoeutectic) and 3 (eutectic) at. % Ni containing alloys while further addition of Ni resulted in the coarsening of eutectic Al3Ni precipitates. All coatings contained γ-Al2O3 phase while additionally, α-Al2O3 phase formed on pure Al and Al-1Ni alloy. Despite the presence of Ni in the coatings, a Ni-based oxide phase was not evident. Ni, as an alloying element, is found to decrease microhardness and thickness of the coatings, induced a thickness variation between the regions close to the edge and center of the samples. This edge effect was maximum on eutectic alloy, which consisted of homogeneously distributed fine Al3Ni precipitates. To investigate the relationship between eutectic precipitate size and the edge effect, Al-3Ni alloy was heat-treated at 620 °C for 168 h and subsequently coated by PEO. Heat-treatment almost eliminated the edge effect, increased the average coating thickness and promoted the α-Al2O3 formation. Fine eutectic morphology in Al-Ni alloys is found to be detrimental for the coatings produced by PEO.

Towards high strengthening efficiency by in-situ planting nano-TiB networks into titanium matrix composites

The coarsening of the matrix microstructure and hybrid reinforcements caused by the excessive-high sintering temperature has been a widespread problem for powder metallurgical titanium matrix composites (TMCs). In this study, inspired by the unique eutectic precipitation path in Ti–B system, we innovatively proposed a new strategy to optimize the microstructure by in-situ planting nano-TiB networks into the composite powder. During the hot-pressing process, the pre-planted networks significantly refined the matrix grain and assembled the special interfacial/intragranular structure, containing interfacial submicron-TiB and intragranular nano-TiB. The well-designed TiB/IMI834 composites exhibited a great improvement in mechanical properties, the compressive yield strength was improved to 1438 MPa with an increase of 24.5%, and the tensile strength at 600 °C was increased to 825 MPa, superior to many thermo-mechanically processed TMCs. The grain refinement and the interfacial/intragranular nano-TiB both contributed to the high strengthening efficiency. This new strategy provided a controllable and facile way to refine the microstructure and achieve high strengthening efficiency in TMCs.

On the elimination of solidification cracks in fusion welding of Al7075 by TiC-nanoparticle enhanced filler metal

Solidification cracks in fusion welding of high strength and precipitation hardened aluminum alloys have been a major challenge for many years. In this research, the weldability of 3-mm thick Al7075 sheets in fusion arc welding was investigated. Welding was conducted with (heterogeneously) and without (autogenously) TiC-nanoparticle enhanced Al7075 filler metal. Results show that the nanoparticles were effective in eliminating welding solidification cracks completely. Two mechanisms are proposed: (1) TiC nanoparticles act as nucleants in the early stage of solidification to alter the microstructure from dendritic to equiaxed and to refine the grains; (2) TiC-nanoparticles act as nucleants in the late stage of solidification to change the shape of eutectic precipitates from continuous to discontinuous and to promote the formation of the Al-Cu-Mg phase at the expense of the deleterious Mg(Cu,Zn)2 (η) phase. Tensile mechanical properties of autogenous weld could not be obtained due to large solidification cracks. In contrast, the heterogenous joint showed relatively good tensile strength and ductility that, however, were slightly lower compared to unwelded Al7075. This was directly linked to the high amount of porosity in the fusion zone due to the use of non-optimal welding parameters adopted in this study to promote solidification cracking for better comparative study and investigation of effects of nanoparticles.

Effect of (NbTi)C Particles on the Microstructure and Hardness of High Chromium and Nickel Indefinite Chilled Cast Iron

High chromium and nickel indefinite chilled cast iron (ICCI), as an excellent hot roll material, is the preferred roll variety due to its good combination of surface roughness, hot crack resistance, and hot wear resistance. The microstructure and hardness of ICCI roll materials with different contents of (NbTi)C particles is studied here, and the microstructure evolution process is analyzed by X-ray diffraction. The influence of (NbTi)C particles on the carbide morphology and distribution is investigated by metallographic microscopy and scanning electron microscopy, and the existence of (NbTi)C particles is observed. The experimental results show that (NbTi)C particles are present in granular, rod, and polygonal forms. Combined with a Thermo-Calc solidification phase diagram, it is found that the (NbTi)C particles undergo eutectic precipitation in the melt, forming short rod-shaped (NbTi)C carbides with a size of about 10 μm. Through the Rockwell hardness test, it is found that the hardness after adding 0.8 wt % (NbTi)C particles was 54.4 HRC, which was 21.1% higher than that without the addition.

Is Thermal Analysis Able to Provide Carbon and Silicon Contents of Cast Irons?

The determination of silicon and carbon contents by thermal analysis is based on the recording of a cooling curve of a melt whose eutectic solidification takes place in the metastable system. The temperatures of the austenite and eutectic arrests are evaluated and then related to the carbon and silicon contents by linear relationships that would be defined by the phase diagram if there were no undercoolings. However, published experimental values of austenite liquidus arrest and metastable eutectic arrest both show significant undercoolings when compared to the equilibrium metastable Fe–C–Si phase diagram. The undercooling of the austenite observed in hypo-eutectic alloys can be explained by tip undercooling during dendritic growth. On the other hand, it is pointed out that alloys with a composition close to the stable eutectic—either slightly hypo- or slightly hypereutectic—can show much higher undercoolings than expected if some stable eutectic precipitates. For such compositions, the thermal analysis could hardly be reproducible enough if the alloy does not solidify completely in the metastable system. Furthermore, the published experimental information on the temperature of the metastable eutectic is here supplemented by new results for silicon contents up to nearly 4 wt%. Both previous and new results show a similar undercooling of 5 to 15 °C compared to the calculated equilibrium metastable eutectic. Each foundry wishing to use thermal analysis for carbon and silicon evaluation must determine its own relationships for austenite liquidus and metastable eutectic to account for the specificity of its melting process and casting system. Care should be taken to avoid any graphite precipitation in the thermal cup, and testing should be performed to improve reproducibility as this defines the accuracy of the composition determination.

Refinement mechanism of cerium addition on solidification structure and sigma phase of super austenitic stainless steel S32654

• Ce addition could modify MgO and MnS into Ce 2 O 3 and Ce 2 O 2 S in S32654. • Ce addition leads to noticeable refinement of both dendrite structure and σ phase. • Effective Ce-bearing inclusions could serve as nucleation cores of γ and σ phase. • Solute Ce markedly enhances undercooling degree, further refining dendrite structure. • Solute Ce promotes σ phase nucleation, while dendrite refinement limits its growth. The influence of Ce addition on the solidification structure and σ phase of super austenitic stainless steel S32654 was systematically investigated via microstructural characterization and thermodynamic calculation. The results indicate that a small addition of Ce could modify MgO and MnS into Ce-bearing inclusions Ce 2 O 3 and Ce 2 O 2 S. Ce addition led to noticeable refinement of both the dendrite structure and σ phase. The refinement mechanism could be attributed to the combined actions of effective Ce-bearing inclusions and solute Ce. Effective Ce-bearing inclusions could serve as heterogeneous nucleation cores of austenite as well as σ phase, which provided a favorable prerequisite for their refinement. Solute Ce significantly enhanced the undercooling degree of the system, further promoting dendrite structure refinement. Meanwhile, solute Ce improved the eutectic precipitation conditions of σ phase and further promoted its nucleation, while the dendrite refinement limited its growth space. Finally, more fine and dispersed σ phase particles formed in S32654 with Ce addition. The refinement of dendrite structure and σ phase will reduce the temperature and time required for high-temperature homogenization, which is beneficial to the hot working of this steel.

Structural and tribological properties of the re-casted dental NiCrMo alloy

The crisis related to the COVID 19 pandemic caused an increase in nickel prices on the global markets. From this perspective, it seems promising to search for the possibilities of effective recycling of nickel-based alloys as biomaterials. The topic of the recasting of Ni-Cr dental alloys is currently being broadly described in the literature. Nonetheless, there are still no conclusive results on the impact of recasting on the quality of the cast dentures. Considering the aforementioned, for research, the effect of recasting on the wear resistance and microstructure of NiCrMo dental alloy was investigated. The Heraenium NA alloy was used for testing. Abrasion resistance was tested by the ball on disc method. Microstructure and wear trace were observed using an optical microscope and a scanning electron microscope. The tests showed a higher wear resistance of the re-casted material. The average coefficient of friction for the initially cast alloys was 0.664, while for the remelted samples the mean value was 0.441. The tested samples are characterised by an abrasive-adhesive wear mechanism. Piling up of the wear tracks edges was observed – the highest for H100. For the H100 samples, a slightly lower average hardness value (HV10) was observed – 226 compared to 233 (HV10) for the samples made from the re-casted alloy (H0). The presence of a dendritic structure of alloys was demonstrated. Blocky eutectic precipitations are visible against the matrix. The observed growth of interdendritic precipitations constitute a natural barrier for the counterpart material and increases its tribological properties. Obtained results suggest that alloy recasting does not constitute a limitation to its use.

Characteristics of microstructure, phase composition and hardening features of steel N8G6M3FTB obtained by a flux-cored wire containing particles BN, TiB2, ZrB2

A research of structure, phase composition and durometric properties transformations as a result of aging of steel N8G6M3FTB deposited by a flux-cored wire containing boron nitride, titanium diboride and zirconium diboride is conducted. It is indicated that the optimal mode of heat treatment of this steel is aging at the temperature of 773 K within 2 h, which provides a hardening effect of 20 HRC. It has been established that the structure of steel consists of cells. The cells are surrounded by eutectic precipitates. The precipitates contain borides and intermetallics. The martensite matrix inside the cells is hardened by numerous precipitates of nitrides, intermetallic compounds, and borides. Upon that, the hardness of steel reaches 60 HRC, that allows to use such steel as wear-resistant.

Hot cracking in ZK60 magnesium alloy produced by laser powder bed fusion process

Additive manufacturing of ZK60 alloy by laser powder bed fusion (LPBF) has promising prospect for light-weight structures and biodegradable implants. Though hot cracking of ZK60 has been widely reported during welding processes, it is surprisingly that no literature so far mentioned it during the LPBF. This paper identified serious solidification and liquation cracking in ZK60 LPBF samples. Low-melting eutectic precipitation was characterized as Mg7Zn3 along the cracks. Ruptured by thermal stress, solidification cracking occurred in the depositing layers due to the wide solidification range, while liquation cracking occurred in the deposited layers due to repeated heating. The two types of cracks merged into a connected network, which hugely deteriorated the relative density of LPBF samples.

Age hardening heat treatment behavior of as-cast Mg–Zn–Al alloys

Magnesium alloys have generated renewed interest as a light alloys; replacing some conventional structural materials for weight reduction in applications like aerospace, automotive and electronics industries. In interior components and powertrains, cast alloys are widely used and represent more than 99% of magnesium alloys used today, whereas only a few wrought products are used. Mostly in automotive applications, Mg-engine block can noticeably reduce the weight and consequently its fuel consumption and environmental impact. Due to solid-state precipitates, these alloys are strong in nature and are produced by an age-hardening heat treatment process. In the present work the age hardening behavior of the as cast Mg–Zn–Al alloys (ZA85 alloy) in the composition of 8 wt. %Zn, 5 wt. %Al has been investigated. Through the differential thermal analysis (DTA) studies, it has been found out that dissolution temperature of ternary eutectic precipitates is present in the alloy. Based on the DTA results, the as cast samples have been solutionised at 360 °C temperature for different intervals of time. Solutionising time has been optimized from the enthalpy values of un-dissolved precipitates. The solution treated samples have been then aged at temperature of 180° C for different time intervals. From the peak hardness values, the ageing conditions have been optimized.