Solidification Of Alloys Research Articles

Microstructural and mechanical properties of Al-Al2O3 micro and nanocomposite fabricated by stir casting

ABSTRACT The current study examines the relationship between the microstructure and tribological characteristics of Al-Si alloy composites reinforced by secondary phase nano SiC particulates synthesis via the stir casting process. The results of wear testing of stir-cast SiC metal matrix composites including up to 12 weight percent fine (75–100 µm) and coarse (125–150 µm) size particles were obtained from cast aluminium alloy. It was discovered via microstructural investigation that the aluminium alloy and SiC particles have good interface bonding. However, at greater amounts (12 wt.%) of fine size reinforcement, clustering of reinforced particles is observed. In addition, results state that finer size particles agglomerate more in the matrix than coarser size particles at greater reinforcement levels. In addition, increasing the amount of SiC particles in the matrix enhanced the hardness of the base alloy. However, when the size of the SiC particles was reduced, the hardness of the composite increased dramatically. Better wear resistance was observed for higher SiC reinforcement levels, while higher forces were also associated with a corresponding increase in wear rate. A combined mode of adhesive and abrasive wear mechanisms is responsible for composite wear, according to a scanning electron microscopy (SEM) investigation of worn surfaces.

Synthesis of Copper–Nickel and Iron–Nickel Alloys by Hydrogen Reduction of Mixtures of Metal Oxide Powders

The vast majority of metals production is based on the use of carbon as a reductant and/or a heating fuel. This results in a large amount of carbon dioxide emissions and should be minimized to limit global warming. In this study, powders of copper–nickel alloy and iron–nickel of varying compositions were produced in a single step by reduction of mixtures of Cu2O-NiO and Fe2O3-NiO powders, respectively, using hydrogen as a reductant. Reduction was performed in a horizontal tube furnace at 700 °C for 45 min. All processing was in the solid state and alloys were produced directly from elemental metal oxides. Exhaust gases were analyzed using a gas analyzer to measure the water content to track the progress of the reduction. Reduction was declared complete when the water content in exhaust gases matched the level before hydrogen was introduced. Both copper–nickel and iron–nickel alloys were produced successfully. X-ray diffractometry confirmed the absence of oxides in the product and the presence of solid phases in agreement with the relevant binary phase diagram. Energy-dispersive X-ray spectroscopy in a scanning electron microscope showed macroscopic homogeneity at the expected composition for each powder mixture directly after reduction, with microscopic fluctuations of the order of several mass percent, within the limits of fluctuations observed following typical casting processes. These promising results warrant further investigation to apply this concept to more chemistries and to scale up the process to a pilot scale.Graphical

Impact of activation energy and cross-diffusion effects on 3D convective rotating nanoliquid flow in a non-Darcy porous medium

PurposeThis study aims to investigate numerically the impact of the three-dimensional convective nanoliquid flow on a rotating frame embedded in the non-Darcy porous medium in the presence of activation energy. The cross-diffusion effects, i.e. Soret and Dufour effects, and heat generation are included in the study. The convective heating condition is applied on the bounding surface.Design/methodology/approachThe control model consisted of a system of partial differential equations (PDE) with boundary constraints. Using suitable similarity transformation, the PDE transformed into an ordinary differential equation and solved numerically by the Runge–Kutta–Fehlberg method. The obtained results of velocity, temperature and solute concentration characteristics plotted to show the impact of the pertinent parameters. The heat and mass transfer rate and skin friction are also calculated.FindingsIt is found that both Biot numbers enhance the heat and mass distribution inside the boundary layer region. The temperature increases by increasing the Dufour number, while concentration decreases by increasing the Dufour number. The heat transfer is increased up to 8.1% in the presence of activation energy parameter (E). But, mass transfer rate declines up to 16.6% in the presence of E.Practical implicationsThe applications of combined Dufour and Soret effects are in separation of isotopes in mixture of gases, oil reservoirs and binary alloys solidification. The nanofluid with porous medium can be used in chemical engineering, heat exchangers and nuclear reactor.Social implicationsThis study is mainly useful for thermal sciences and chemical engineering.Originality/valueThe uniqueness in this research is the study of the impact of activation energy and cross-diffusion on rotating nanoliquid flow with heat generation and convective heating condition. The obtained results are unique and valuable, and it can be used in various fields of science and technology.

Sulphuric precipitates in novel titanium-based, sulphur-bearing bulk metallic glass – a BMG composite?

ABSTRACT New titanium-based metallic glasses containing sulphur as a key element have recently been developed and are the subject of ongoing research related to the effects of sulphur introduction into glass-forming alloy systems. Here we report on the formation of sulphuric precipitates during solidification of a Ti40Zr35Cu17S8 alloy and on the occurrence of secondary intermetallic compound crystallization starting in sulphur-depleted zones around the precipitates. The alloy is a promising metallic glass for use as a structural and biomedical material as it shows a high yield strength and good corrosion resistance paired with a low density. The role of sulphur for the glass formation in the Ti-Zr-Cu-S system is discussed and specimens quenched into different structural states are investigated by means of high-energy synchrotron diffraction and electron microscopy. The electron microscopic findings reveal that sulphuric precipitates precede the crystallization of an intermetallic (Ti, Zr)2Cu phase, which is the primary phase when sulphur is not present in the system and thus lead to a higher glass-forming ability. The sulphuric precipitates are found in specimens of various casting thickness and differ in their volume percentages depending on the size of the cast sample, while the secondary phase (Ti, Zr)2Cu crystallizes heterogeneously in the interfaces between the sulphuric precipitates and the local matrix.

Simultaneously enhancing mechanical and tribological performance in undercooled Co-18.5 at. % B alloys

The wear behavior and its mechanism greatly depend on the microstructure of alloys. Herein, the Co-18.5 at. % B eutectic alloys with three different morphologies and phase constitutions were obtained by undercooling solidification under different magnetic field intensity (0T, 10T, 20T), and the relative mechanical properties and tribological performance were investigated systematically. Results show that the grain size of Co–B alloy decreases first and then increases with the increase of magnetic field strength, the average grain size of samples under 0 T and 20 T was about 3–5 μm, while the grain size of sample with 10 T refined to 20–40 nm. The sample treated under 10 T exhibits the lowest wear rate (1.53 × 10−5 mm3N−1m−1) and highest micro-hardness (868.27 HV). The fine grain strengthening effect is the main reason for the increase in strength and hardness of Co–B alloy. The fine crystalline nano-heterostructures (20–40 nm) and the precipitation enhancement of secondary precipitated Co nanoparticles also has a beneficial effect on mechanical properties. The oxide friction layer consisting mainly of layered H3BO3 lubricant, detected on the worn surface of Co–B alloy (10T) has anti-wear properties. By contrast, Co–B alloys with coarse Co3B grains (0T) and inhomogeneous FCC-Co/Co2B lamellar structure (20T) present higher wear rates and lower hardness. This work can provide guidance for the initial control of mechanical properties from the design of the microstructure.

Effects of interrupted aging T6I4 on hardness and fracture toughness of aeronautic AA7050 alloy

Effects of interrupted aging T6I4 on hardness and fracture toughness of aeronautic AA7050 alloy

Selective microzone remelting to reduce and refine the coarse primary carbides in high-carbon alloy steels

The coarse primary carbides in high-carbon alloy steels can significantly impair their overall performance. Reducing and refining the primary carbides efficiently are always of great significance in material processing. Here, an innovative approach ― the selective microzone remelting (SMR) method, is proposed to dramatically reduce and refine the coarse primary carbides. The method is achieved by utilizing an electric current and is facilitated with the substantial difference in electrical resistivity between carbides and the matrix phase. When a sample contains massive coarse primary carbides is subjected to an electric current, the high electrical resistivity of carbides leads to the selective remelting of local carbides before the sample reaches solidus temperature during heating while during cooling the big difference in electrical resistivity suppresses the carbides formation but promotes the austenite nucleation and growth. This mechanism has been validated through the successful treatment of M50 bearing steel, in which the large-sized blocky primary carbides were eliminated completely, leaving only small-sized eutectics with extremely thin lamellas. Besides, the microporosity in the as-cast sample has also been reduced significantly via SMR treatment. These studies demonstrated that the proposed SMR treatment can be a promising method to reduce and refine coarse precipitates formed during solidification in various alloys.

Bridging molecular dynamics and additive manufacturing: A study of Al-12 at% Si alloy solidification dynamics

This manuscript provides a detailed analysis of the molecular dynamics of the directional solidification process in Aluminum-Silicon (Al-12 % at Si) alloys, with a particular emphasis on applications in additive manufacturing. Utilizing molecular dynamics (MD) simulations, the study examines large systems containing 5–15 million atoms to investigate various facets of the solidification process. These include the dynamics of interface motion and the formation of Silicon (Si) precipitates. The research reveals significant variations in interface velocities and orientations across different thermal gradients and growth rates, underscoring the intricate interaction between thermal and solute flows in the microstructural development of Al-Si alloys. These findings are vital for comprehending and refining the solidification process in additive manufacturing, ultimately enhancing the mechanical strength and reliability of the final products. The paper highlights the critical role of microstructure control in printed metals and proposes future research directions, aiming to apply these insights to more complex alloy compositions and manufacturing contexts. In the concluding phase, the scikit-image library was employed to analyze dendritic formations in solidifying Al-Si alloys using MD simulations. This analysis delineates trends in dendritic count, spacing, perimeter, and area over time, offering essential perspectives on the solidification process and its implications for the alloy's microstructure and mechanical characteristics. The Si content in the Al-Si alloy used can be considered eutectic in the solidified structure. Si atoms are predominantly located at grain boundaries and precipitate regions. Coordination number analysis further confirms the presence of Si in these locations. This microstructure, characterized by a primary Al/Al-Si matrix and Si-rich eutectic regions, aligns with experimental observations in rapid solidification processes in additive manufacturing.

Toward a Standardized Approach for Characterizing β‐Fleck Defects in Titanium Alloys

β‐flecks are a type of segregation defect commonly encountered during the solidification of titanium alloys enriched with β‐stabilizing elements. These defects are associated with a detrimental impact on mechanical properties, which potentially limit the service life of parts containing them. Despite their significance, a standardized method for identifying these defects is lacking. In this study, a systematic approach is provided to detecting and characterizing β‐flecks in a representative metastable β‐Ti alloy and β‐C (ASTM Grade 19/Ti–3Al–8V–6Cr–4Mo–4Zr). By combining low temperature but prolonged aging, time‐dependent etching, and Fiji‐assisted image analysis, the presence and characteristics of β‐flecks are determined with precision and impartiality. This straightforward technique offers a reliable means for visualizing and quantifying β‐flecks in titanium alloys. It establishes a foundational framework that can be broadly applied to various β‐Ti alloys prone to β‐fleck formation.

Microstructure and mechanical properties of CoCrNiVAlx multi-principal component alloy

Multi-principal component alloy has been proved to form disordered solid solution in most cases. However, multi-principal component alloy with single phase solid solution has a few disadvantages in mechanical properties, such as low strength or poor plasticity. Aiming at CoCrNi-based multi-principal component alloy with low strength, this paper proposed a method to enhance the multi-principal component alloy through composition design. CoCrNiVAlx multi-principal component alloy was melted by non-consumable vacuum arc melting, and the content of σ phase in the multi-principal component alloy was changed by adjusting the content of Al element. With the addition of Al element, the fcc disordered phase in the multi-principal component alloy gradually went to the ordered L12 phase with the same structure. When the amount of Al was 1.5 wt%, the compressive strength reached 2347 MPa and the hardness reached 760.8HV, which were 30% and 20% higher than the compressive strength (1828 MPa) and hardness (619.3HV) of CoCrNiV multi-principal component alloy, respectively. With the further increase of Al element to 2.0 wt%, the σ phase in the multi-principal component alloy increased further, resulting in the simultaneous decrease of strength and plasticity. The strengthening mechanism of multi-principal component alloy was analyzed, and the strengthening action of L12 phase was confirmed. The results showed that the strengthening of multi-principal component alloy was mainly provided by L12 phase strengthening (1229.55 MPa, 52.39%) and grain boundary strengthening (376 MPa, 16.02%). This paper provided a probable strategy to increase the strength of the multi-principal component alloy, which opened up a new idea for the composition design of multi-principal component alloy.

Comparative analysis of microstructural, compositional, and grazing incidence characteristics of oxide scale on 316L steel: SLM vs. wrought conditions

The aim of this research is to compare the oxidation behavior and characteristics of oxide scale of 316L steel produced by two methods: selective laser melting (SLM) and conventional casting and forming (wrought). To this end, the initial composition and microstructure of samples produced by those methods were first studied. Thermogravimetric analysis (TGA) and long-term isothermal oxidation tests were carried out on the samples and the oxidation kinetics were compared. The oxidized samples were then examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and grazing incidence X-ray diffraction (GIXRD). The results indicated that in the temperature range of 600 °C–900 °C, the oxidation resistance of the SLM alloy is lower than that of the wrought alloy, especially at 800 °C. This is attributed to the combined effect of: i) smaller grain size due to the rapid solidification in the SLM alloy that increases the paths of oxygen penetration, ii) lower presence of chromium and manganese elements in the oxide layer and iii) preferential growth of iron oxide in the form of hillocks on the surface. Surface and cross-section analysis of the oxide layers show that iron oxide is dominant on the surface of the SLM sample at temperatures of 600 °C and 800 °C, and at 800 °C its extended hilly growth leads to significant spallation of the oxide scale and an exponential increase in the oxidation rate. However, at 900 °C, with the formation of a continuous oxide layer containing Fe2MnO4 and CrMnO4, the oxidation rate significantly decreases in both alloys.

Influence of hardening on mechanical properties of hard alloy VK8

Influence of hardening on mechanical properties of hard alloy VK8

Microstructure and fracture toughness of laser wire deposited Ti-6Al-4V

In this paper, the microstructure, and mechanical properties of Ti-6Al-4V fabricated through Laser Directed Energy Deposition (L-DED) process are investigated and discussed. Deposited coupons were produced on Ti-6Al-4V wrought substrate using Ti-6Al-4V ELI grade wire with the laser wire deposition (LWD) process. Characterization efforts led to the evaluation of the microstructure, hardness, tensile behavior, and fatigue crack growth resistance of the build-up alloy. Microstructure of the deposit consists of columnar prior β grains and basket-weave α/β phase mixture. The size of the alpha laths is measured as 1.2 ± 0.3 µm and 0.8 ± 0.2 µm in the banded zone and band-free zone, respectively. Hardness of the deposited block is found to be uniform and ranging between 321 and 323 Hv. Tensile and fatigue crack growth properties of the deposited block were evaluated in various orientations. Tensile specimens loaded in the deposition direction exhibited 824 MPa and 930 MPa for yield and ultimate tensile strength, respectively. Tensile specimens loaded in the build direction exhibited 782 MPa and 907 MPa for yield and ultimate tensile strength, respectively. The analysis reveal that the tensile properties of the deposited material match the strength requirements for ASTM F1108 Cast Ti-6Al-4V. However, they fell just below the AMS 4911P Wrought Ti-6Al-4V standard. Fatigue Crack Growth Rate tests were conducted for three directions: parallel to the deposition direction, parallel to the build direction and at 45° of the deposition direction. No significant differences in crack growth properties were observed between the different orientations with average crack initiation near threshold (ΔKth) and the fracture toughness (Kc) value of 3.6 MPa√m and 69 MPa√m, respectively. The crack propagation properties are similar to cast & wrought materials.

Numerical simulation of melt flow and heat transfer in casting filling process based on SPH

There is a great influence of the melt filling process on the quality of castings. Smoothed particle hydrodynamics (SPH) that materials are approximated by free particles rather than by fixed grids is applied to accurately predict fluid flows involving complex free surfaces. In this paper we present a mathematical model of melt flow and heat transfer by using SPH method. A novel approach is used in the governing equations to ensure stable numerical schemes and homogeneous particle distributions. The SPH heat equation takes into account the thermal release during phase transition and is more suitable for alloy solidification. The solid wall boundary conditions are slightly modified to satisfy the filling simulations. Several case studies are carried out to predict significant details about the filling order and flow structures in the mold cavity. The velocity and temperature distributions during different stages of melt filling are also given. The results show that this proposed model allows us to understand the predisposition of defects such as gas porosity and weld lines in the castings. These predictions can be used as inputs for improving process parameters, venting and cooling systems design.

Microstructural and photocatalytic properties of nanostructured near-β Ti-Nb-Zr alloy for total hip prosthesis use

With its unique corrosion resistance, light weight, mechanical strength, and biocompatibility, TNZ is a versatile metal alloy that is used in the aerospace and medical industries. The current study aims to investigate the effect of milling time (2, 12, 24, and 36 h) on the nanostructured ternary alloy Ti-25Nb-25Zr (TNZ) prepared by high energy ball milling, a process involving the use of a high-energy ball mill to mix and grind the alloy powders, on its structural, physical, and photocatalytic characterizations. The alloys' characteristics, such as morphology, structural properties, relative density/porosity, surface roughness, hardness, and Young's modulus, were evaluated using SEM, XRD, surface profilometer, and microdurometer, respectively. The photocatalytic characterization was conducted by measuring their absorbance as a function of time using a spectrophotometer of visible and ultraviolet light in the wavelength range of 250–650 nm. Results showed that the crystallite and mean pore size reduced with increasing milling time, with the smallest values of 25 nm and 34 μm, respectively, after 36 h. This indicates that longer milling times result in a more compact and uniform structure, which could enhance the mechanical properties of the alloy. Structural characterization shows that the amount of the β-Ti phase increased with increasing milling time, resulting in the spherical morphology and texturing of the synthesized alloys. The milled alloys' structural evolution and morphological changes were sensitive to their milling times. Also, the relative density, Young's modulus, and hardness increased, reaching values of 89 %, 105 GPa, and 352 HV, respectively, due to grain size decreasing with increasing milling time. This suggests that longer milling times lead to a denser and harder alloy, which could be beneficial for its use in total hip prostheses. The photocatalytical characterization demonstrated that the degradation of orange II (OII) increased with increasing milling time. The Ti-25Nb-25Zr catalyst gave the best degree of degradation, which meant that the decolorization process could be operated rapidly and at a relatively low cost without UV irradiation.

Influence of Friction Stir Processing on the Hardness and Tribological Properties of Aluminium-Magnesium Alloys

Influence of Friction Stir Processing on the Hardness and Tribological Properties of Aluminium-Magnesium Alloys

An investigation on the wear resistance and mechanism of Fe60-xCo20MoxNi20 (x=10, 15, 20) high-entropy alloy reinforced by μ-phase

Fe–Co–Ni face-centered cubic (FCC) alloy has been one of the most extensively investigated alloys due to its potential ductility and toughness, while its low yield strength and wear resistance limit the engineering application. In this study, the different Mo content is added in the Fe–Co–Ni based alloy to solve this problem. The microstructure, wear resistance and tribological mechanism of Fe60-xCo20MoxNi20 (x = 10, 15, 20) high-entropy alloys after different annealing treatments are systematically investigated. The results reveal that the content of the μ phase increases with the addition of Mo element when annealed at 600 °C, and the highest amount of the μ phase is observed in the Mo20 alloy. The formation of the μ phase enhances the hardness of the Mo20 alloy, reduces the surface roughness during the wear process compared to Mo10 and Mo15 alloys, thereby improving the wear resistance. Furthermore, increasing annealing temperature also affects the content and distribution of the μ phase. The Mo20 alloy annealed at 600 °C exhibits the best wear resistance. However, as the annealing temperature increases to 1000 °C, the wear resistance deteriorates due to the spalling of the μ phase. In contrast, the wear resistance of the Mo15 alloy is optimized due to the uniform distribution of the μ phase. Additionally, when the sliding force increases from 2 N to 10 N, the wear resistance of the Mo20 alloy initially deteriorates before improves. This is mainly due to the increase in abrasive wear when the load is increased from 2 N to 5 N, while as the sliding force further increases to 10 N, a glaze layer is formed on the wear surface, which produces a lubricating effect. Furthermore, the better wear resistance of Mo20 and Mo15 alloys compared with others can also be attributed to the friction subsurface with nano-scale structure.

УПРОЧНЕНИЕ МЕТАЛЛОРЕЖУЩЕГО ИНСТРУМЕНТА ЭЛЕКТРОИСКРОВОЙ ОБРАБОТКОЙ

Metal-cutting tools during the machining of parts by cutting experience high strength and thermal loads, causing wear of the cutting edges. Increasing the wear resistance of the cutting edges of a metal-cutting tool is an urgent task. (Research purpose) The research purpose is analyzing the causes of wear of end mills and drills and proposing the most rational method of hardening metal-cutting tools. (Materials and methods) End mills and drills were chosen as the object of research. The BIG-5 installation with the use of electrodes made of hard alloys VK8 and T15K6 was used to harden metal-cutting tools. It was pointed out that relatively mild electrical modes with pulse energy from 0.05 to 0.2 joules are used to harden drills and end mills, the thickness of the applied coating layer in such modes is 10-30 micrometers. (Results and discussion) It was noted that the performed analysis of the applied hardening methods confirmed the feasibility of using electric spark processing for these purposes. The optimal modes of electric spark processing were selected on the basis of previous studies. Comparative tests for wear resistance of samples from materials of end mills (P18) and drills (P6M5) were performed. It was shown that when using electrodes made of T15K6, the wear resistance of the samples increases by 1.85 times for P18 and by 8 times for P6M5. Comparative tests of hardened end mills and drills for wear resistance were carried out. The indicator was the number of processed parts. (Conclusions) The result of using the electric spark processing method to harden the cutting tool was an increase in the life of end mills by 3.8 times, drills by 2.25 times. The productivity of manufacturing parts has increased.

Optimization of V-Ti-Fe hydrogen storage alloy based on orthogonal experiments

Vanadium-based solid solution hydrogen storage alloys have attracted much attention because of their high hydrogen capacity, mild hydrogen absorption- desorption conditions, and high safety. However, the V-Ti-Fe alloys, developed at low cost, have a relatively low effective capacity and is unsuitable for practical production. In this work, (VxFe100-x)100-yTiy-z%Ce (x=0.83,0.85,0.87; y=16,18,20; z=1,2,3) alloys are designed by orthogonal method to investigate the effect of compositions on the microstructure and hydrogen storage properties. It is shown that the effective hydrogen capacity and desorption plateau pressure of the (VxFe100-x)100-yTiy-z%Ce alloy are related to multiple factors, such as lattice constants, tetrahedral interstitials of the BCC and BCT phases, electron concentration and Vickers hardness. The optimized alloy (V87Fe13)82Ti18-1 %Ce based on the orthogonal experiments shows a reversible hydrogen storage capacity of 2.17 wt% and a desorption plateau pressure of 0.373 MPa at 70°C. The reversible hydrogen capacity of (V87Fe13)82Ti18-1 %Ce is superior to most V-Ti-Fe alloys.

Enhancing Tribological Performance of Micro-Arc Oxidation Coatings on 6061 Aluminum Alloy with h-BN Incorporation

Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves into the impact of h-BN nanoparticles into MAO coatings on their structure, corrosion resistance, phase composition, and tribological properties. The results show that the incorporation of h-BN particles reduces the porosity and surface roughness of the coating while enhancing its hardness and wear resistance. The best corrosion resistance is obtained at a concentration of 2 g/L h-BN. An analysis of worn surface morphology, corrosion resistance, and friction coefficient change was conducted to evaluate the performance of this coating. This method provides a new approach to enhance the surface hardness and wear resistance of aluminum alloys, which is significant for expanding the application of aluminum alloys in corrosion environments.