Metallurgical Transition Research Articles

Achieving the Superior Abrasive Wear Resistance in ZTAP/Fe Composites from the Theoretical Calculations Guided Designing of Metallurgical Interface Transition Layer

Using the first-principles calculations and phonon QHA method, the thermodynamic stability, mechanical and thermophysical properties of binary Ni-Ti phases are obtained. The most thermodynamically feasible binary Ni3Ti phase with a superior elasticity and mechanical tensile strength is designed as the interfacial transition layer between ZTA ceramic particles and iron matrix. A high-Cr white cast iron matrix composite reinforced with ZTA particles is fabricated via infiltration casting process. The microstructures and three-body abrasive wear resistance of the composite are investigated. The obtained ZTAP/Fe composite has a compact metallic Ni3Ti metallurgical transition layer with a small amount of AlNi2Ti and TiO phases in the interfacial region, leading to a strongly adhesion between iron matrix and ZTA ceramic particles due to the presence of covalent Ti-O, Fe-O and Zr-O bonds. The composite exhibits the relative wear resistance 12.9 times higher than that of reference Cr15 specimen. The wear mechanism of the ZTAP/Fe composite is mainly attributed to the removal of iron matrix under the SiO2 abrasives, as revealed from the secondary electron images and laser scanning confocal topography.

High temperature oxidation resistance and thermodynamic properties of (TaNbZr)N and (TaNbZr)C quaternary ceramic coating

A TaNbZr-based quaternary ceramic coating with a metallurgical transition layer on a titanium alloy surface has been produced. The quaternary ceramic coatings exhibit a face-centered cubic structure and distinct structural orientation. The introduction of carbon and nitrogen significantly improved high-temperature oxidation resistance compared to metallic coatings in cyclic oxidation tests. Specifically, the (TaNbZr)N coating provided effective thermal protection during 800 °C cyclic oxidation for 100 hours (10 cycles). The phase stability and evolution of quaternary ceramic coatings were clarified using in-situ XRD. Further, first-principles calculations elucidated the enhanced thermal stability and high-temperature performance of (TaNbZr)N and (TaNbZr)C coatings.

Microstructure and mechanical properties of a semi-centrifugal compression processed Al6013 and Cu bimetal

Abstract In this study, aluminum Al6013 and copper (Cu) cylindrical bimetal was manufactured by means of an original production method. The optical microscope and scanning electron microscope (SEM) images of the bimetal material produced through this approach, semi-centrifugal compression, were used in microstructural investigations following which metallurgical transition zones were defined. Through an energy dispersive X-ray (EDX) analysis of the defined regions, the chemical content of the regions were determined. Micro hardness values of the regions were determined and comparisons were made with the chemical content and hardness values of the materials used in the bimetal production before the manufacturing process. In addition, the mechanical properties of the materials were compared by applying tensile tests to the bimetallic components Cu and Al6013 and to the bimetal material produced. In the light of the values obtained, the general properties of the bimetal material produced through this new approach were presented.

Optimization of process parameters in friction stir welded dissimilar magnesium alloys using RSM

The welding of two dissimilar magnesium alloys is considered as a greatest challenge because of poor metallurgical transition at joints. The FSW process is mostly used for joining different metals which are very difficult to weld through fusion welding technique. In this study the FSW process is used to weld AZ31B and AZ91C magnesium alloys. Three different tool profile (Conical, square and cylindrical type) were used along with three different rotational speeds (900, 1150 and 1400 rpms) and tool traverse speeds (25, 35 and 45 mm/min). The tensile strength was experimentally calculated for all the 15 combinations given by the Box – Behnken model in response surface methodology technique. Three samples in each combination were tested and the average tensile strength was used to find the optimized welding parameters combination in response surface methodology software. The microstructure of the welded region was analysed using scanning electron microscopy to verify the effect of brittle inter – metallic transition at welded joints. The regression equation generated from the Box – Behnken model was used to find the optimized parameters condition. The optimized tensile strength value of 186.721 was obtained from Response Surface Methodology at an optimum parameter combination of a tool rotation speed at 900 rpm with square tool pin head of 45 mm tool traverse speed. The conformal experiment was performed to verify the accuracy of the optimized parameter combination. The conformity test results showed a tensile strength of 182.57 MPa with an error percentage of 2.2% from proposed optimization value which confirms the scope of this study in end functional applications.

The Integration of Process and Product Metallurgy in Niobium Bearing Steels

A review of the technological integration of both the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels have evolved into the development of higher quality steels for more demanding end user requirements. The connection of process and physical metallurgy is evolving through the integration of research that is aimed at improving product quality. However, often the connection of the process metallurgical parameters is not reported, especially with industrial data. The importance of this innovative metallurgical connection is validated by the market demand for reduced fuel consumption, improved quality, and CO2 emissions in both the automotive and construction sectors. This situation has further increased the demand for new higher quality Nb-bearing steel grades. This integrative process/physical metallurgical (IP/PM) approach applies to both low and high strength steel grades in numerous applications. Often, the transition from laboratory melted and TMCP to the production scale is challenging. The methodology, process control, and key production steps that are required during the melting, ladle metallurgy, continuous casting, thermal, and hot rolling production conditions often vary significantly from the laboratory conditions. Understanding the reasons and corrective action for these variations is a critical product development success factor. These process metallurgy parameters for the industrial melting, casting, reheating, and hot rolling of Nb grades are connected and correlated to the resultant microstructures, physical metallurgy, and mechanical properties. These advanced high strength steels are microalloyed with Nb, V, Ti and/or other elements, which affect the austenite-ferrite transformation. Niobium enables the achievement of substantial grain refinement when the plate or sheet is rolled with the proper reheat, hot reduction, and thermal schedule. A recently developed key metallurgical transition is in progress applying this integrative approach with the use of MicroNiobium. A reduction of Mn and C levels with the complementary refinement of the microstructural grain size through MicroNiobium additions improves the robustness of the steel to better accommodate some process metallurgy variations. Applications are evolving in lower strength steels with Nb to achieve complementary grain refinement.

Copper isotopes as a means of determining regional metallurgical practices in European prehistory: A reply to Jansen

We present a detailed response to the critique by Mr. Jansen of the paper “Digging Deeper: Insights into Metallurgical Transitions in European Prehistory through Copper Isotopes”. When we consider Cu isotope ratios of European Eneolithic and Early Bronze Age artifacts in the context of their local geological settings, climates, and archaeological contexts, Mr. Jansen's hypothesis that 63Cu enrichment results from the adoption of fahlore ores is untenable. In both Serbia and Central Europe, the earliest copper production is associated with 65Cu-enriched ores and subsequently produced artifacts yield lower ranges δ65Cu. This shift in Cu isotopic composition correlates with the initial use of predominantly hypogene ores, not with variations in their trace element content. Essentially the expanded dataset supports the conclusions that were presented in the original paper—Cu isotopes are an effective means of delineating the transition from oxide-based smelting to methodologically more complex smelting of sulphide ores in prehistoric Europe with its relatively limited production and trade. Mixing did not mask the critical Cu isotope signatures in this setting. Therefore, Cu isotope compositions of artifacts can be used to interpret the mineralogical character of the ores from which they were produced, regardless of their provenance, as long as trade networks remained within a region of similar climatic history.

Digging deeper: Insights into metallurgical transitions in European prehistory through copper isotopes

Southeastern Europe is the birthplace of metallurgy, with evidence of copper smelting at ca. 5000 BCE. There the later Eneolithic (Copper Age) was associated with the casting of massive copper tools. However, copper metallurgy in this region ceased, or significantly decreased, centuries before the dawn of the Bronze Age. Archaeologists continue to be debate whether this hiatus was imposed on early metalworking communities as a result of exhaustion of workable mineral resources, or instead a cultural transition that was associated with changes in depositional practices and material culture. Copper isotopes provide a broadly applicable means of addressing this question. Copper isotopes fractionate in the near-surface environment such that surficial oxide ores can be differentiated from non-weathered sulphide ores that occur at greater depth. This compositional variation is transferred to associated copper artifacts, the final product of the metallurgical process. In the central Balkans, a shift from 65Cu-enriched to 65Cu-depleted copper artifacts occurs across the metallurgical hiatus at the Eneolithic-Bronze Age boundary, ca. 2500 BCE. This indicates that the reemergence of metal production at the beginning of the Bronze Age is associated with pyrotechnical advancements that allowed for the extraction of copper from sulphide ore. Thus copper isotopes provide direct evidence that the copper hiatus was the result of exhaustion of near-surface oxide ores after one-and-a-half millennia of mining, and that the beginning of the Bronze Age in the Balkans is associated with the introduction of more complex smelting techniques for metal extraction from regionally abundant sulphidic deposits.

Effects of the pouring temperature on the formation of the bonding zone between AZ91 and AlSi17 in the compound casting process

The compound casting process was used to join AZ91 magnesium alloy to AlSi17 aluminium alloy. Liquid AZ91 was poured onto a solid AlSi17 insert placed in a steel mould heated to 370 °C. The experimental results showed that the temperature of the AZ91 melt affected the formation of the bonding zone between the two alloys. A continuous bonding zone was formed by applying a pouring temperature of 650 °C. The use of higher temperatures, i.e. 680 °C and 700 °C, did not lead to the formation of a continuous metallurgical transition zone at the AZ91/AlSi17 interface. The bonding zone was analysed using an optical microscope and a scanning electron microscope equipped with an energy dispersive X-ray (EDS) detector. The structural constituents of the bonding zone near the AlSi17 alloy were: an Al3Mg2 intermetallic phase, primary Si particles surrounded by a rim of an Mg2Si intermetallic phase and fine Mg2Si particles. The area of the bonding zone that was adjacent to the AZ91 alloy had a eutectic structure composed of an Mg17Al12 intermetallic phase and a solid solution of Al and Si in Mg.

Failure analysis and metallurgical transitions in SS 304L air pipe caused by local overheating

AISI 304 type stainless steels are widely used for structural parts in power stations due to their excellent resistance to creep and corrosion at elevated temperatures. In an incident at one of IEC's (Israel Electric Corporation) power stations, an air pipe made of AISI 304L Stainless Steel which was part of a gas conditioning system conducting hot air for mixing with natural gas, failed and cracked at two points. Failure analysis included stereo imaging, optical metallography, SEM/EDS/EBSD and magnetic tests. It was revealed that one crack occurred due to high-temperature overload and the other due to creep, showing grain coarsening and secondary phase formations respectively to an extent that is entirely atypical under standard working conditions. A follow-up investigation was conducted in order to gain further insight into the processes and conditions that led to the two crack failures in the pipe. Thermal treatments of intact specimens from an undamaged pipe area were conducted at different temperatures and times. Pipe specimens subject to heat treatments of 650°C resembled material near the creep fracture in the field pipe. Pipe specimens subject to heat treatments of 1000°C and 1150°C resembled material near the high-temperature overload failure. The thermal treatment was followed by microstructural, mechanical, compositional and phase analyses.

Numerical simulation and optimization of WC-SS420 induction brazing process

Tungsten carbide (WC) is a very hard, brittle, and relatively expensive cermet. It is often joined to more economical material, such as martensitic 420 stainless steel (SS420), to form a hybrid cutting tool stock. This article summarizes a study on the optimization of an induction brazing process joining these two materials using BAg-22 as filler metal. This study uses an integrated approach consisting of finite element analysis (FEA) modeling and experimental verifications. The thermal behaviors and the metallurgical transitions during the brazing cycles of WC-BAg22-SS420 joints are studied. This study investigated process and metallurgical issues due to mismatches in thermal expansion coefficient, thermal conductivity, and electromagnetic permeability. Using the optimum process parameters derived from simulation, joint strengths exceeding 370 ± 40 MPa for shear were obtained. The hardness of WC was unaffected by the brazing heat. However, softening in the SS420 next to the fusion interface was constantly observed in the experiments. The FEA modeling results demonstrated that using a controlled heating and cooling process schedule was effective in mitigating this softening phenomenon. Experimental verification of this mitigation method is currently under study.

A shape memory alloy microvalve with flow sensing

A Nitinol™ actuated silicone tubing microvalve is combined with a downstream thermocouple forming an integrated system for the control and metering of microliter volumes. The integrated device is of a normally closed design having a break pressure of more than 68.9 kPa (517 mmHg), dimensions on the order of 1 mm × 2 mm × 2 mm, inert fluid contact surfaces, and senses flow. Power pulses of 213 mW are required for 2.5 s response times. Opening of the valve is brought about by a temperature induced metallurgical transition of a short piece of nitinol wire with a diameter of 75 μm. The force generated by the transition is harnessed in order to stretch microbore silicone tubing away from a luminal plug (synthetic ruby ball), thus forming flow channels. Actuation is performed using a pulsed paradigm with a distinctive on and off period enabling flow sensing capabilities. The integrated thermal principle flow sensor operates by sensing the peak temperature derivative of a transient thermal pulse in the flow stream imparted by joule heating of the nitinol wire when actuated. It was found that this flow sensing scheme proved to be a reliable method of detecting valve performance changes over time. The system is constructed using readily available commercial components including microbore silicone tubing, nitinol shape memory alloy (SMA) wire, a miniature synthetic ruby ball, and a thermocouple.

Comparison of Hardness Enhancement and Wear Mechanisms in Low Temperature Nitrided Austenitic and Martensitic Stainless Steel

ABSTRACTEnergetic nitrogen implantation into austenitic stainless steel or nickel alloys leads to the formation of a very hard and wear resistant surface layer with an expanded lattice, while similar results are reported for selected martensitic steels. A comparison of the phase formation under identical process conditions at 380 °C using an austenitic (304) and a martensitic (420) steel grade (in an annealed ferrite/cementite condition) shows that the initial microstructure is retained in both of them. As the formation of dislocations and stacking faults cannot account for the dramatic hardness increase, the build-up of compressive stress is proffered as an explanation covering these two steel types. Furthermore the energetic nitrogen implantation apparently stabilizes the expanded lattice with suppressing the chemical transition to iron nitrides and, for steel 420, the metallurgical transition towards austenite at high nitrogen contents.

Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)

Abstract

Correlation of interfacial structure and microstress of yttrium-modified ion-plated titanium nitride film with its adhesion property

The adhesion performance of ion-plated TiN yttrium-modified Ti(Y)N films to a mild steel (A3 steel) substrate have been evaluated by means of constant-rate tensile tests and scratch tests. Interface studies were carried out using transmission electron microscopy, and the microstresses in the films were measured using X-ray line profile analysis. The results show that Ti(Y)N film exhibits an excellent adherence to the substrate, which may be a result of the modification of yttrium at the interface so as to form a very good metallurgical transition bond.

MODIFICATION OF MICROSTRUCTURE AND PROPERTIES OF ION PLATED TITANIUM NITRIDE FILM BY ADDING YTTRIUM

The microstructure and properties of ion plated titanium nitride film can be improved by adding rare earth element yttrium. Y-modified titanium nitride (Ti(Y)N) film exhibits an excellent corrosion resistance and binding strength to the substrate of A3 steel. The microstructure characteristics of Ti(Y)N/A3 system have been investigated by X-ray diffraction, ion probe mass analysis and cross section transmission electron microscopy. The results show that yttrium is enriched at the interface of Ti(Y)N/A3 system and the modification of Y at the interface leads to a very good metallurgical transition band from the substrate to the film and the preferential orientation along close-packed TiN(lll) crystal plane, which may be the major reasons for the improvement of the properties of the Ti(Y)N film.

Properties of red light emitting (Al, Ga)As double heterostructure diodes

en

Factors influencing doping control and abrupt metallurgical transitions during atmospheric pressure MOVPE growth of AlGaAs and GaAs

Atmospheric pressure MOVPE of GaAs and AlGaAs has been investigated using two gas handling systems and a conventional horizontal reactor. Initially a simple source/carrier gas manifold design was assessed but severe retention of reagents in the pipework resulted in poor control of doping and interface abruptness. However, integration of the reagent and carrier gas in a pressure balanced vent/run configuration gave a significant improvement. AlGaAs/GaAs multilayers and n +/n - GaAs transitions have been used to assess the performance of both systems. Abrupt p-type doping transitions using bis-cyclopentadienylmagnesium proved unsuccessful as long doping tails were observed.

The potential and electric field at the metallurgical boundary of an abrupt p-n semiconductor junction

Analytical equations are presented that rigorously establish the electrostatic potential and electric field at the metallurgical transition point of an abrupt p-n semiconductor junction. From these equations, the classical depletion-layer approximation is shown to be rigorously correct only when (N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> = N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> ), although this solution remains adequate for engineering purposes if 1.0 ≤ N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> / N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> ≤ 10.0, approximately. It is also shown that mechanisms of operation take place within an asymmetrical abrupt junction (N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> ≥ N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> ) that cannot be deduced from the depletion-layer aproximation. For example, the asymmetrical junction is shown to contain an electrostatic potential and an electric field at its metallurgical transition point that are essentially constant throughout a wide range of reverse biasing voltage. These characteristics imply that the total electrostatic charge within its p-type and n-type space charge layers remain essentially constant, and that its p-type space-charge layer is of constant width, despite the application of a reverse biasing voltage. These heretofore unreported mechanisms of operation arise from a layer of mobile charge carriers residing at the low-doped side of the metallurgical transition between n-type and p-type semiconductor material.