Modification of 316L steel powders with bronze using high energy ball milling for use as a binder component in PBF-LB/M printing of diamond-metal matrix composites

For the processing of diamond-metal matrix composites, the powder bed fusion using a laser for metals (PBF-LB/M), represents a new promising method for the additive manufacturing of diamond tools for concrete and rock machining, even with more complicated geometries. Previous research activities show a strong tendency for cracking and delamination during the construction process of the samples. This behavior is caused by thermal residual stresses associated with the embedded diamonds. To control these negative effects on the process side, the volume energy density is reduced accordingly, which, however, led to increased pore formation. This publication deals with an approach on the material side to modify a 316L stainless steel base powder with an addition of 20 wt% bronze via a high energy ball milling (HEBM) process in such a way that a homogeneous solid solution phase is created. A significantly increasing of the melting interval and a decreasing of both solidus and liquidus temperature was observed, which can reduce pore formation in the PBF-LB/M-process. In addition, XRD-diffractometry and SEM/EDS-analysis showed that the homogeneous solid solution phase of this alloyed powder segregates again into Fe- and Cu-rich phases when heated up to the melting point

Mechanistic Undrestanding Of Amorphization In Iron-Based Soft Magnetic Materials

Iron-based magnetic alloys possess very good magnetic and mechanical properties. Among these alloys Fe-Si-B-based alloys show outstanding saturation magnetization and coercivity which makes them great candidates for many industrial applications. Addition of certain elements to the Fe-Si-B base is proven to improve the homogeneity and fineness of microstructure as well as enhance the magnetic behavior of these alloys. In this research work, we have studied the effect of adding copper and niobium to the Fe-Si-B base alloy. Previous studies have shown that magnetic alloys show better magnetic properties when their microstructure consists of nanocrystals embedded in an amorphous matrix. In order to reach amorphization, magnetic alloys are traditionally melted and then cooled down very fast to prevent crystallization and grain growth in their microstructure. However, there are several disadvantages associated with this method of fabrication, such as the limitation in thickness of the products. To solve this issue, we proposed a new method of fabrication for magnetic alloys where amorphization occurs through mechanical alloying, and the amorphous powder alloy that is produced by this process is then consolidated using a technique called spark plasma sintering finding appropriate mechanical alloying processing parameters to get an amorphous structure. Many different processing parameters were investigated, and the mechanical properties, microstructure, and magnetic properties of all samples were examined. The effect of spark plasma sintering processing parameters on samples sintered from the amorphous powders was then studied. Finally, the amount of energy introduced to the powder from the milling balls during the mechanical alloying process was calculated. We were able to find a trend between the energy introduced to the powder during the milling process and the amorphous structure of the milled powders. From our data, we draw an energy map that shows the window of total energy in which the powder, regardless of the mechanical alloying processing parameters under which it was milled, will show an amorphous structure. This area has not been explored for these magnetic alloys before, and this data can be used by researchers who are trying to obtain amorphization via the mechanical alloying process

Phase Evolution During Mechanical Milling of Pre-alloyed Gas Atomized Maraging Steel Powders and Magnetic Characterization

Maraging steels are an important class of high strength steels that exhibit an exciting combination of magnetic and mechanical properties. Past research work, specifically on the magnetic properties, focused on improving the magnetic properties of the bulk form of the steel, fabricated by conventional materials processing and manufacturing. With the recent focus towards additive manufacturing, it is imperative to investigate the structure and magnetic properties of the maraging steel powder and the influence of temperature. In this thesis work, firstly, the structural and magnetic characterization of a commercially available pre-alloyed gas atomized powder was investigated. It comprised of primarily the martensite phase (α) and a small amount of austenite (γ). The powder particle size characteristics, D90 of the as-received powder was estimated as ~21 μm. The saturation magnetization (MS), intrinsic coercivity (HCI), and remanent magnetization (MR) of the as-received powder, at ambient temperature, was ~176 Am2/kg, ~3 kA/m, and ~1.4 Am2/kg, respectively. Thermal treatment of the powder up to 900 K for ~1 h showed an inappreciable change in MS, while the coercivity decreased, suggesting good magnetic properties and promising opportunities to reuse the powder. Subsequently, phase evolution during mechanical milling of the pre-alloyed powder was investigated. Powder milled from 3 h to 8 h comprised nanocrystalline martensitic phase. The estimated grain size was as low as ~20 nm. The MS, HCI, and MR ranged between ~164 Am2/kg and ~169 Am2/kg, ~4.9 kA/m and ~6.7 kA/m, and ~3.4 Am2/kg to ~3.9 Am2/kg, respectively. Milling more than 8 h resulted in the formation of austenite and extraneous intermetallic phases, resulting in the reduction of MS and increase in HCI. At cryogenic temperatures (60 K-300 K), MS (0) (MS at 0 K) and maximum magnetic moment per atom (μH) of the nanocrystalline milled maraging powders were ~ 178 Am2/kg and ~ 1.83 μB, respectively. The thermally treated maraging steel powders retained the nanostructure, and their MS and HCI were comparable to as-received powder.Master of Science in EngineeringMechanical Engineering, College of Engineering & Computer ScienceUniversity of Michigan-Dearbornhttps://deepblue.lib.umich.edu/bitstream/2027.42/150650/1/Ganesh Varma Thotakura - Final Thesis.pdfDescription of Ganesh Varma Thotakura - Final Thesis.pdf : Thesi

Effect of process control agents used in mechanochemical synthesis on properties of the prepared composite reactive materials

The study explores synthesis and reactivity of new reactive materials prepared by ball milling. High-energy ball milling became a ubiquitous mechano-chemical tool to manufacture diverse powders, from pharmaceuticals or foods to alloys to new solid rocket propellants. It enabled a dramatic expansion of the range of chemical compositions obtainable; however, it did not so far, allowed one to fine-tune morphology or interfaces in the generated powders. It is shown in this work how different process control agents (PCAs) can serve to tune the powder morphology and reactivity. Commonly used as lubricants and cooling agents during milling, liquid PCAs can be used as an effective tool in modifying both chemistry and morphology of mechanochemically prepared reactive materials. For example, a polar, non-oxidizing fluid, e.g., acetonitrile, can reduce the size of aluminum particles, but more interestingly, it can modify their surface to enable new redox reaction pathways leading to accelerated ignition and combustion. Using such modified aluminum in a composite prepared by milling makes it possible to design unusual reactive materials. Materials with the same chemical compositions, and thus the same overall energy densities can be made with controllable reaction dynamics and tunable heat release. Thus, it becomes possible to separate the effects of chemical composition and interface structure on the reaction mechanisms and rates. An even more unusual capability of manipulating shapes and sizes of the synthesized powders is discovered in this study when liquid PCA comprises two immiscible fluids. A complex system including an emulsion combined with suspended particles is generated inside the milling vial. When such a system is milled, solid particles can be refined, mixed, and eventually accumulated inside the droplet phase. Thus, spherical solid aggregates are formed with narrow size distributions. Milling conditions can be found to tune size, density, and porosity of such spheres. Produced narrowly-sized spherical powders are attractive because of their dramatically improved flowability. The existing methods for synthesizing spherical powders (e.g., spray-drying, extrusion-spheronization, droplet-melting) are more expensive, time-consuming, and energy-intensive. Unlike milling, they cannot be employed to a diverse range of materials and the challenges associated with wide particle size distributions often are unsurmountable. Our approach has been validated experimentally for elemental (e.g., Al, B), alloyed (B-Ti, Al-Ti), ceramic (Fe2O3), organic (melamine), and composite (Al-CuO) spheres from materials with a broad range of initial particle sizes and mechanical properties. The average size of the particles could be selectable from 5 to 200 µm. Experiments also confirmed superior rheological properties of the prepared reactive powders and their enhanced reactivity. For future, this study can be expanded beyond reactive materials to discover a new generation of value-added materials for catalysts, adsorbents, and feedstock powders for additive manufacturing

Synthesis and Characterization of Al-4.5%Cu Alloy Powder Using Mechanical Alloying

The present work aims to improve the mechanical properties of Duralumin (Al-4.5 wt. % Cu) alloy produced by mechanical alloying and consolidated using conventional isotactic hydraulic compressor. A uniform dispersion of SiC and TiO2 reinforcements tends to improve the mechanical properties of the present alloys. The current alloys show xtraordinary hardness values which are 1-1.5 times higher than the conventional duralumin alloys. For this purpose, pure elemental powders of Al and Cu were blended and milled in a planetary ball mill and sintered at 550°C for 1 hour in Argon atmosphere. XRD and SEM of samples collected at different stages during milling and after sintering were done to determine the phase evolution and microstructural morphology of the current alloys. The crystallite size, lattice strain and lattice parameters were analyzed by Williamson-Hall method. The crystallite size decreases rapidly up to 7 hours of milling and becomes almost constant with further milling. Addition of SiC (5 and 10 vol. %) and TiO2 (5 and 10 vol. %) as reinforcements in the matrix improves the hardness. Addition of SiC reinforcement leads to better dispersion than TiO2 as evident from the hardness values. This is due to the higher modulus of elasticity of SiC which is almost double than that of TiO2

Nano-engineering of composite material via reactive mechanical alloying/milling (RMA/M)

Attempts to strengthen a chromium-modified titanium trialuminide by a combination of grain size refinement and dispersoid strengthening led to a new means to synthesize such materials. This Reactive Mechanical Alloying/Milling process uses in situ reactions between the metallic powders and elements from a process control agent and/or a gaseous environment to assemble a dispersed small hard particle phase within the matrix by a bottom-up approach. In the current research milled powders of the trialuminide alloy along with titanium carbide were produced. The amount of the carbide can be varied widely with simple processing changes and in this case the milling process created trialuminide grain sizes and carbide particles that are the smallest known from such a process. Characterization of these materials required the development of x-ray diffraction means to determine particle sizes by deconvoluting and synthesizing components of the complex multiphase diffraction patterns and to carry out whole pattern analysis to analyze the diffuse scattering that developed from larger than usual highly defective grain boundary regions. These identified regions provide an important mass transport capability in the processing and not only facilitate the alloy development, but add to the understanding of the mechanical alloying process. Consolidation of the milled powder that consisted of small crystallites of the alloy and dispersed carbide particles two nanometers in size formed a unique, somewhat coarsened, microstructure producing an ultra-high strength solid material composed of the chromium-modified titanium trialuminide alloy matrix with small platelets of the complex carbides Ti2AlC and Ti3AlC2. This synthesis process provides the unique ability to nano-engineer a wide variety of composite materials, or special alloys, and has shown the ability to be extended to a wide variety of metallic materials

Nanostructured Mg-ZK50 Sheets Fabricated for Potential Use for Biomedical Applications

Magnesium (Mg) alloys are widely used in biomedical applications thanks to their combination of exceptional mechanical properties, biocompatibility, and biodegradability. Mg-ZK alloy series; for instance, ZK40, ZK60 and ZK61; is an example of the most commonly used Mg bio-alloy. Zirconium (Zr) acts as a grain refiner when added to Mg, which manipulates the material structure by producing a refined internal structure and enhancing its properties. In addition, when Zinc (Zn) is added to a Mg-Zr alloy, strength is improved. Therefore, given the favorable properties of ZK alloys in biomedical applications, the current research aimed for the fabrication and the evaluation of a new ZK alloy with a new composition; ZK50, as a potential biomaterial for biomedical applications. Three stages were implemented in order to achieve the objective of this study. In the first stage, ball milling process was used to synthesize nanostructured Mg-ZK50 alloy from elemental powders (Mg, Zr, and Zn). The produced powders (BM) were studied using SEM, XRD and TEM to determine the internal structure refinement as well as the phase development due to milling. In the second stage, Powder-in-Tube (PIT) rolling process followed by annealing was applied to produce consolidated thin sheets from the BM powders. Accordingly, in the third stage, the effect of annealing on the internal structure, mechanical properties, corrosion behavior and cytotoxicity was evaluated. The mechanical milling of the elemental powders produced a nanostructured alloyed powder after 45 hrs of milling with a crystallite size of 8.83 nm, which is considered the finest internal structure for Mg and Mg based alloys to date. Afterwards, nanostructured thin sheets were successfully produced using PIT at 300 °C with 67% reduction percent. The modulus of the sheets was found matching to that of human bones. It is worthy to note that annealing was found to have a detrimental effect on the corrosion behavior of the alloy. However, a hydroxyapatite layer was formed which indicated that the produced sheets induced osteoinductivity of the bone. Moreover, cytotoxicity of the sheets was not affected by the sheets and all the produced sheets showed an acceptable toxicity level within the cells. In conclusion, the produced Mg-ZK50 nanostructured alloyed sheets are considered a new potential biomaterial for orthopedic implants that induces osteoinductivity and prevent stress shielding

Effect of milling Time on the Structure, Micro-hardness, and Thermal Behavior of Amorphous/Nanocrystalline TiNiCu Shape Memory Alloys Developed by Mechanical Alloying

Cataloged from PDF version of article.In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti-41Ni-9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0-12 h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19') and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time. (C) 2013 Elsevier Ltd. All rights reserved

Mechanical Alloying: Processing and Materials

Mechanical alloying is a technique of producing alloys and compounds that permits the development of metastable materials (with amorphous or nanocrystalline microstructure) or the fabrication of solid solutions with extended solubility. The elements or compounds to be mixed (usually as powders) are introduced in jars usually under a controlled atmosphere. Regarding the scope of this book, advanced materials have been developed by mechanical alloying: Fe–X–B–Cu (X = Nb, NiZr) nanocrystalline alloys, mixtures of the binary Fe–Mn and Fe–Cr alloys with chromium and manganese nitrides, Mn–Al–Co and Mn–Fe alloys, non-equiatomic refractory high-entropy alloys, nanocrystalline Fe–Cr steels, nanaocrystalline Mn–Co–Fe–Ge–Si alloys, Al–Y2O3 nanocomposite, and hydride-forming alloys. Likewise, production conditions and ulterior treatments can provide readers interesting ideas about the procedure to produce alloys with specific microstructure and functional behavior (mechanical, magnetic, corrosion resistance, hydrogen storage, magnetocaloric effect, wastewater treatment, and so on). As an example, to obtain the improvement in the functional properties of the alloys and compounds, sometimes controlled annealing is needed (annealing provokes the relaxation of the mechanical-induced strain). Furthermore, the powders can be consolidated (press, spark plasma sintering,and microwave sintering) to obtain bulk materials

Synthesis of Al-Si-Ni Nanostructured Materials by Mechanical Alloying

An effort has been made to synthesize Al-based nanostructure by mechanical alloying (MA). Elemental powder of Al, Si and Ni were blended to obtain nominal composition of Al75Si15Ni10. Alloying was carried out in a high energy planetary ball mill using stainless steel grinding media at 300 r.p.m. up to 50 h. Toluene was used as the process control agent (PCA). The ball to powder weight ratio was maintained at 10:1. The phase evolution of the milled samples was studied by X-ray diffraction (XRD) analysis. The microstructural characterization of the milled powder was followed by scanning electron microscopy (SEM) and XRD. Dissolution of Si and Ni in Al was found to be 15% and 10% respectively along with the formation of some intermetallic phases. SEM micrographs showed that the powder morphology was changed from coarse layered structures obtained by very short period of milling to finer as the milling time increased. XRD and energy dispersive X-ray analysis (EDX) showed the formation of a homogeneous solid solution of the above said blends after milling for 50 h. The crystallite size, lattice strain (%) and lattice parameter were calculated from major XRD peaks. It shows that the crystal size decreased very rapidly up to 25 h of milling and then slowly became almost constant with further milling, whereas, lattice strain (%) increased gradually up to 25 h very rapidly and then very slowly became nearly constant with progress of milling. This suggests that major structural changes and dissolution of the alloying elements almost completed by 25 h, and further milling refined the product by MA. The lattice microstrain of the material increases exponentially. It increases rapidly up to 25 h and then increased slowly as the milling progresses further. The change of lattice parameter of Al-rich solid solution showed a rapid decrease throughout the process of MA. This is because of the entrance of Si and Ni atoms into the lattice of the Al which causes distortion in it. The change in the above mentioned parameters were determined up to 30 h of milling as on further milling Al peaks vanishes because of formation of partially amorphous structure along with some intermetallic phases