Melting Metallurgy Research Articles

Processing of Niobium-Alloyed High-Carbon Tool Steel via Additive Manufacturing and Modern Powder Metallurgy.

Niobium is recently considered one of the potential alloying elements for tool steels due to the formation of hard and stable carbides of MC type. Its use is limited by the fact that these carbides tend to coarsen during conventional melting metallurgy processing. This work explores the potential of additive manufacturing for processing Nb-alloyed tool steel with a high content of carbon. Directed energy deposition was used as the processing method. It was found that this method allowed us to obtain a microstructure very similar to that obtained after the use of consolidation via spark plasma sintering when subsequent heat treatment by soft annealing, austenitizing, oil quenching and triple tempering for secondary hardness was applied. Moreover, the soft annealing process could be skipped without affecting the structure and properties when machining would not be required. The hardness of the steel was even higher after additive manufacturing was used (approx. 800-830 HV 30) than after spark plasma sintering (approx. 720-750 HV 30). The wear resistance of the materials processed by both routes was almost comparable, reaching 5-7 × 10-6 mm3N-1m-1 depending on the heat treatment.

Ultra-fast fabrication of Bi2Te3 based thermoelectric materials by flash-sintering at room temperature combining with spark plasma sintering

Highly crystalline Bi2Te3 based compounds with small grain size were successfully synthesized by flash sintering (FS) method in 10 s at room temperature under suitable current density using Bi, Te and Se powders. The instantaneously generated local Joule heat at grain boundary is regarded as the main reason for the rapid completion of chemical reaction and crystallization. By combining FS synthesis method with spark plasma sintering (SPS), Bi2Te3 based bulk materials with high relative density were fabricated in 10 min. Suitably prolonging sintering temperature and holding time in SPS process can decrease carrier concentration and phonon thermal conductivity, while increasing carrier mobility. Hence, the sample prepared at 753 K for 3 min shows 20% higher ZT value than that of the sample prepared at 723 K for 3 min. Compared with common zone melting or powder metallurgy methods taking several hours by complex operation, this method is time-saving and low cost.

Determination of RuAl phase boundaries in binary Ru–Al phase diagram at room temperature and 1200 °C

Abstract Binary Ru–Al alloys with nominal compositions from 29.39 at.% Al up to 60.47 at.% Al were manufactured by powder-metallurgy processing. Single-phase RuAl with a homogeneous microstructure was prepared which is difficult to achieve by melting metallurgy. The microstructure and lattice parameters of the alloys were investigated by optical and scanning electron microscopy, energy-dispersive spectroscopy, wavelength-dispersive spectroscopy and X-ray diffraction. The parametric method was employed to determine the RuAl phase boundaries. Single-phase RuAl was found to exist from near-stoichiometry up to 53.8 at.% Al at room temperature and up to 54.5 at.% Al at 1200 °C, respectively. In addition, the phase Ru2Al3 was found to be stable at room temperature and to have a very narrow range of stoichiometry.

Stress corrosion studies of AL 2014 alloy using synthesized pyrimidin derivative inhibitor in different concentration of HCl solution

The stress corrosion resistance of AL 2014 in high temperature acidic media usingthe inhibitors MPPA and AMPO has been evaluated using an autoclave. The liquid melt metallurgy technique using vortex method was used to fabricate AL 2014 alloy. Stress corrosion tests were conducted using weight loss method for different exposure time, normality and temperature of the acidic medium. The corrosion rates of AL 2014 alloy was lower to that of Concentration increases of the inhibitor.

Development of TiAl-Si Alloys-A Review.

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods.

Structure and Properties of Cast Ti-Al-Si Alloys.

Intermetallic compounds based on Ti-Al- (Si) are attractive materials with good thermal stability and low density. However, the production of these materials is quite complicated. Partially modified conventional methods of melting metallurgy are most often used due to availability, possible high productivity, and relatively low production costs. Therefore, some technologies for the production of intermetallics based on Ti-Al are currently available, but with certain disadvantages, which are caused by poor casting properties or extreme reactivity of the melt with crucibles. Some shortcomings can be eliminated by modifying the melting technology, which contributes to increasing the cost of the process. The work deals with the preparation of Ti-Al-Si intermetallic compounds with different contents of aluminum and silicon, which were produced by centrifugal casting in an induction vacuum furnace Linn Supercast-Titan. This process could contribute to the commercial use of these alloys in the future. For this research, the TiAl15Si15(in wt.%) alloy was selected, which represents a balanced ratio of aluminides and silicides in its structure, and the TiAl35Si5 alloy, which due to the lower silicon content allows better melting conditions, especially with regard to the melting temperature. This alloy was also investigated after HIP (“Hot Isostatic Pressing”) treatment.

Stress Corrosion Studies of AL 2014 Alloy Using Synthesized Pyrimidin Derivative Inhibitor in Different Concentration of HCl Solution

The stress corrosion resistance of AL 2014 in high temperature acidic media using The inhibitors MPPA and AMPO has been evaluated using an autoclave. The liquid melt metallurgy technique using vortex method was used to fabricate AL 2014 alloy. Stress corrosion tests were conducted using weight loss method for different exposure time, normality and temperature of the acidic medium. The corrosion rates of AL 2014 alloy was lower to that of Concentration increases of the inhibitor.

Studies on the corrosion resistance of Al7075 / SiC metal matrix composites in an alkaline environment

Metal matrix composites are of interest every day due to their lightweight, improved mechanical properties, and increased corrosion resistance. They are used in the aeronautical, aerospace, marine, and automotive industries. A variety of methods can estimate Their corrosion properties. The open-circuit potential studies are also a tool for evaluating the corrosion of composite materials. This research paper focuses on studying open circuit potential determination of the aluminium 7075 alloys reinforced with silicon carbide particulate in differently concentrated sodium hydroxide solutions. The composite materials were prepared by adding 2, 4, 6, 8 and 10 weight percentages of silicon carbide to the aluminium base metal liquid melt metallurgy technique (Vortex method). The silicon carbide used as reinforcement in size range of 50 – 80 µm, which is commercially available. The SiC particulates material is had been preheated to 400°C and introduced into the liquid melt of Al7075 at a rate of 100 g/m, under constant agitating condition using a mechanical stirrer system for 3 to 4 minutes. Rectangular specimens of 2 cm length, 1cm width and 1 mm thickness were used for the experiments. 1sq.cm area of the specimens was exposed to sodium hydroxide medium. Open circuit potential experiments test was conducted using a multimeter and calomel electrode system. The potential observed for 2, 4, 6, 8 and 10% silicon carbide composites were less than the potential of matrix alloy for a range of 30 hours.

Thermally sprayed coatings for highly stressed sliding bearings

Sliding bearings have to fulfil various requirements depending on the operating conditions. Conventional sliding bearings, however, cannot be used for critical operating conditions such as frequent acceleration and shut-down procedures or they require the use of complex manufacturing processes and cost-intensive material solutions. For this reason, complex multilayer systems or rolling bearings are currently used for frequent start-up cycles and low relative velocities. New material systems and manufacturing processes are of particular interest in order to operate sliding bearings cost-effectively and reliably even under these increased requirements.Within the scope of this study, new material concepts are developed by thermal spraying. Thermal spraying allows the production of innovative material combinations, which cannot be produced by melting metallurgy. In addition, coatings can be applied by thermal spraying on a wide variety of geometries directly on the bearing support structure, thus achieving increased freedom of design and additional cost savings compared to conventional processes. The coating concepts are based on a cobalt or bronze matrix into which friction-reducing solid lubricants can be integrated during the coating process. One particular goal of the coating concepts is to improve the operating properties under critical conditions, such as low relative velocities and high loads. Therefore, the developed coatings are tested on a modified ring-on-disc tribometer and are compared to a reference sliding bearing material produced by conventional casting. To verify the coating capability, the most promising coating is investigated on a full-scale main bearing test bench of a wind turbine. For the first time, a thermally sprayed coating and a new conical sliding bearing design are evaluated as a substitution for currently used rolling bearings as main bearings in wind turbines. Hereby, it is demonstrated whether these new coating concepts can meet the requirements of this highly stressed bearing position.

Properties Comparison of Ti-Al-Si Alloys Produced by Various Metallurgy Methods.

Melting metallurgy is still the most frequently used and simplest method for the processing of metallic materials. Some of the materials (especially intermetallics) are very difficult to prepare by this method due to the high melting points, poor fluidity, or formation of cracks and pores after casting. This article describes the processing of Ti-Al-Si alloys by arc melting, and shows the microstructure, phase composition, hardness, fracture toughness, and compression tests of these alloys. These results are compared with the same alloys prepared by powder metallurgy by the means of a combination of mechanical alloying and spark plasma sintering. Ti-Al-Si alloys processed by melting metallurgy are characterized by a very coarse structure with central porosity. The phase composition is formed by titanium aluminides and titanium silicides, which are full of cracks. Ti-Al-Si alloys processed by the powder metallurgy route have a relatively homogeneous fine-grained structure with higher hardness. However, these alloys are very brittle. On the other hand, the fracture toughness of arc-melted samples is immeasurable using Palmqvist’s method because the crack is stopped by a large area of titanium aluminide matrix.

Powder metallurgic fabricated plug targets for the synthesis of AlCrSiWN multicomponent coating systems

Monolithic and alloyed targets, conventionally produced by means of melt metallurgy, have been established as conventional target material designs for physical vapor depositions (PVD). However, integrating refractory metals into the sputtering material, leads to restrictions concerning the solubility and phase formation in the target compound. In this context, plug targets are commonly used to deposit multinary coatings with a desired chemical composition. However, producing plugs by means of melt metallurgy restricts the types and amounts of integrated elements.Since current PVD coating concepts aim at an extension of the functionality spectrum by element doping, new target concepts are required. The use of several monolithic targets is one method to produce coatings combining various elements within one coating. Yet depending on the target setup, this approach can result in a nanolaminar coating deposition. To circumvent this, a new production route, which ensures the integration of sintered CrSiW plugs in a monolithic aluminum target, is examined in this study. Two coating deposititons, each with an Al(CrSiW)20 and an Al(CrSiW)48 plug target, were performed by means of direct current (DC) magnetron sputtering and compared with a reference coating, which was synthesized using an AlCr20 target. The dense morphology of AlCrN was significantly changed to a more columnar structure due to slight additions of silicon and tungsten. High aluminum contents in AlCrN and AlCrSiWN, in turn, resulted in a distinct enhancement of the mechanical properties.

Formation of Intermetallics Layers in Ni-Ti System Prepared by Direct Energy Deposition

The Ni-Ti alloys with approximately equiatomic chemical composition are one of the most important materials from the shape memory alloys. Excellent properties such as shape memory effect and superelasticity are based on the phase transformation between austenite and martensite structure of the NiTi phase. In the past the investigation of the preparation methods was focused on melting metallurgy - vacuum induction melting and arc re-melting and powder metallurgy routes like self-propagating high-temperature synthesis, hot isostatic pressing and spark plasma sintering. In the last several years importance of the additive manufacturing has increased significantly. This paper deals with formation of the Ni-Ti intermetallic phases between the nickel and titanium layers deposited on each other by direct energy deposition energy method. The varied mixture of the Ti 2Ni, NiTi and Ni3Ti phases was formed in agreement with the binary Ni-Ti phase diagram. Some problems like cracking and nickel loss have to be solved by preheating of platform or adjustment of laser parameters.

Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles

A robust method is introduced to simulate and study the filler wire metallurgy for controlled cooling conditions after melting, enabling efficient mapping with prompt analysis of trends. Proposed is a reduced, though representative, process with more controllable conditions. Short lengths of filler wires are preplaced in a cavity, drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Pulse shaping influences the cooling rate, granting the ability to tailor weldament microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding, where a representative thermal cycle is needed. For high toughness, a controlled amount of acicular ferrite and, in turn, nonmetallic inclusions is desirable. This “snapshot” method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer, or advanced methods like high speed imaging or modeling. The method offers a wide spectrum of variants and applications.

Effect of Heating Rate on the Phases Formation in Ti-20 wt. % Al Powder Mixture

In this work, the effect of heating rate on the reaction temperatures in Ti-20 wt. % Al powder mixture subjected to reactive sintering process were studied and microstructure, phase composition and porosity of the reaction products were described. This system was studied because the alloys based on Ti-Al intermetallics are modern high-temperature materials and their production by common metallurgical routes is problematic. Reactive sintering could potentially replace currently used method - melt metallurgy. However, many phases form during this process and some of them are undesired. For this reason, it is necessary to describe the temperatures and other reaction conditions of their formation. One of these parameters is a heating rate. The heating rate affects reaction temperatures, phase composition as well as porosity significantly. Therefore, various heating rates were tested and the reaction temperatures were determined. The heating was recorded by optical pyrometer and one exothermic reaction was observed. It was found that this reaction is associated mainly with the formation of Ti3Al phase. Further, it was revealed that porosity decreased with increasing heating rate. This work offers data important for thermodynamic calculation and description of intermetallic phases formation during reactive sintering process.

Effect of Zirconium, Niobium and Chromium on Structure and Properties of Ni-Ti Alloy

This work deals with the possibility of modification of the phase composition and improvement of the properties of the NiTi alloy by alloying with other elements. After the production by conventional melting metallurgy as well as powder metallurgy, the Ni-Ti alloys contain in addition to the NiTi shape memory phase a lot of other phases, for example Ti2Ni, Ni3Ti, Ni4Ti3. Some of these phases can have an undesirable effect on the properties of the Ni-Ti alloy. A possible solution is the addition of alloying elements to destabilize these phases. The aim of this work is to describe the effect of Zr, Nb and Cr as alloying elements in the amount of 1 and 3 wt. % on microstructure, phase composition, hardness and transformation behavior of the Ni-Ti alloy produced by powder metallurgy using reactive sintering. Alloying by chromium leads to increase of hardness and microhardness of the NiTi phase whereas the addition of the alloying elements niobium and zirconium increases the temperatures of phase transformations.

PREPARATION OF TiAl15Si15 ALLOY BY HIGH PRESSURE SPARK PLASMA SINTERING

This work deals with preparation of intermetallic alloy TiAl15Si15 (wt. %) by powder metallurgy using Spark Plasma Sintering method. Ti-Al-Si alloys are known as materials with low density, relatively good mechanical properties in comparison with their density and good oxidation and corrosion resistance at elevated temperatures. Preparation of intermetallics by melting metallurgy is very problematic. Powder metallurgy using reactive sintering followed by suitable compaction seems to be a promising method. In this work, TiAl15Si15 alloy was prepared by reactive sintering, milling and by unique ultra-high pressure Spark Plasma Sintering within the framework of international cooperation in Krakow. For the comparison it was also prepared by conventional Spark Plasma Sintering. The results show that higher pressure of sintering decreases the porosity of compact sample and increases mechanical properties, especially hardness.

Studies of ZA-27 / Red Mud Metal Matrix Composites with respect to Corrosion Properties

Conventional monolithic materials have boundaries in achieving good properties like strength, stiffness, toughness and density. To overcome these weaknesses and to meet the ever increasing demand of modern day technology, composites are most auspicious materials of recent interest. Metal matrix composites are most successful materials used for recent works in the industry. Metal matrix composites own significantly improved properties including high tensile strength, toughness, hardness, low density and good wear resistance compared to alloys or any other metal. They also exhibit increased corrosion resistance. There has been an increasing demand in composites containing low density and low cost reinforcements. In this studies popular alloy of nineties ZA-27 is chosen as matrix and red mud particulates which is obtained as a waste in the aluminium manufacturing industries is selected as reinforcement. Liquid melt metallurgy technique using vortex method is chosen for the manufacture of metal matrix composites. Reinforcement content added to matrix was 2 percent 4 percent and 6 percent. Matrix alloy was also casted in the same way for comparison. Microstructures of the composites and matrix alloy are taken by scanning electron microscope technique after machining. Static weight loss corrosion test and potentiodynamic polarization techniques test using potentiostat were conducted in different concentrations of sodium chloride solutions. Specimens for the tests mentioned already are machined from the castings according to ASTM standards. Corrosion rates were calculated after knowing the weight loss in static weight loss corrosion test. Elico company make Potentiostat / Galvanostat model CL95 was used for the determination of corrosion current and corrosion rate. In all the tests the corrosion current was found to decrease from matrix alloy to 6 percent composite. Corrosion rate was also to be decreased from matrix alloy to 6 percent composite. Hence metal matrix composites made up of ZA-27 as matrix and red mud as reinforcement are more suitable for marine applications and automobile applications in place of matrix alloy.

Evaluation of Corrosion Resistance Properties of Aluminium 7075-Beryl Composite Materials in Acid Chloride Medium

Metal matrix composites are popular now a day due to the fact that their properties can be tailored by the addition of reinforcements like particulates, fibres and whiskers. Metal matrix composites show improved mechanical propertieswhen compared with those of matrix alloy. Improved ultimate tensile strength, hardness, percentage elongation, young’s modulus, impact strength and compression strength are shown by metal matrix composites. In the same way the corrosion resistance properties of composites are also improved over the same property of matrix alloy. Composites show improved weight loss corrosion resistance, stress corrosion resistance and polarisation studies. Hence the composites are important in the fields of aircraft, automobile and marine industries due to their increased life, improved mechanical and corrosion properties. In the present research work, aluminium 7075 alloy is selected as matrix and beryl or beryllium aluminium silicate is selected as reinforcement. Both are commercially available. Metal matrix composites containing different volume fraction of beryl particulates were successfully manufactured through liquid melt metallurgy technique using vortex method. Pre heated but uncoated beryl particulates of 50-80 micro meters are used in the manufacture of composites. Characterization studies were conducted on the aluminium 7075 alloy and its composites samples to evaluate the microstructural properties and corrosion properties. Microstructures were taken by using scanning electron microscope. Microstructural characterizations of composite samples reveal the presence and homogeneous distribution of beryl particulates. The corrosion tests conducted were static weight loss corrosion and potentiodynamic polarisation test using Elico make Potentiostat / galvanostat model CL95. Hydrochloric acid with different concentrated solutions usedas corrosion medium.Hydrochloric acid with three different concentrations of are used for the study. Corrosion current and corrosion rates were determined for matrix and composites in the above mentioned tests. In all the tests the composites decreased corrosion rate and decreased corrosion current when compared to those of matrix alloy. Hence composite materials are more suitable for the different applications than the matrix.

High-Temperature Behaviour of Ti-Al-Si Alloys Prepared by Spark Plasma Sintering

Nowadays, there is effort to substitute in aerospace industry so far commonly used alloys (especially nickel alloys) with new low-density materials, which will have comparable mechanical properties and good resistance against high-temperature oxidation. Ti-Al intermetallic alloys are in this trend modern, already-used material. The results of the tests show that further enhancement of properties can be achieved by addition of silicon. The disadvantage of these materials is a low fracture toughness at room temperature and difficult production. Powder metallurgy seems to be a way to replace still used melting metallurgy. In this work, cyclic oxidation of Ti-Al-Si alloys prepared by reactive sintering, milling and Spark Plasma Sintering is described. The TiAl10Si30 alloy was evaluated as the best alloy from tested ones, because was the most resistant to the stresses. Stress was induced into the oxide layer by repeated annealing and cooling.

Correlation of target properties and plasma parameters in DC magnetron sputtering with Langmuir probe measurements

Utilizing different manufacturing methods for producing sputtering targets leads to significant variations in target microstructure with the latter showing a pronounced impact on the performance of the target in direct current magnetron sputtering (DCMS) in terms of varying sputtering yields. This study aims at correlating measured plasma parameters on the one hand with varying microstructure of molybdenum targets on the other hand. To this end, the sputtering performance of targets manufactured by means of selected powder metallurgy as well as melting metallurgy processes in DCMS is experimentally investigated. Ranging over two orders of magnitude, the mean grain size is identified as the major varying microstructural parameter of the investigated targets. Measurements of spatially varying plasma parameters under steady state sputtering conditions are carried out by means of a Langmuir probe moved over the target at several distances perpendicular to the target top surface. The largest differences in the measured parameters are found in the vicinity of the target surface. In particular, the electron density is found to decrease with increasing mean grain size.