Ultrashort Sintering and Near Net Shaping of Zr-Based AMZ4 Bulk Metallic Glass

The GeniCore Upgraded Field Assisted Sintering Technology U-FAST was applied to the sintering of a commercial Zr-based bulk metallic glass powder AMZ4. The XRD, SEM and DSC analysis of the sintered compacts showed the benefit of the U-FAST method as an enabler for the production of fully amorphous samples with 100% relative density when sintering at 420 °C/480 s (693 K/480 s) and 440 °C/ 60 s (713 K/480 s). The hardness values for fully amorphous samples, over HV1 519, surpass cast materials and 1625 MPa compressive strengths are comparable to commercial cast products. The advantage of the U-FAST technology in this work is attributed to the high heating and cooling rates inherent to ultra-short pulses, which allow to maintain metastable structures and achieve better temperature control during the process. Increasing sintering temperature and time led to the crystallization of the materials. The geometry and material of the dies and punch determine the thermal inertia and pressure distribution inside the compacts, thus affecting the properties of the near net shape NNS compacts made using the U-FAST device.

Microstructure Evolution of (MgCoNiZnCu)O High Entropy Oxides Using Ceramic Injection Molding

Near net shaping ceramic injection molding process of (MgCoNiZnCu)O high entropy oxides were conducted using commercial precursor oxide powders. Through ball milling, internal mixing, injection molding, solvent and thermal debinding as well as final sintering process, the ceramic products would be obtained with little machining. Compacts prepared are single rock-salt phase based on XRD and EDS Mapping results. Meanwhile, with the increasing of sintering temperature from 900 ℃ to 1050 ℃, particle diffusion rate and densification of samples becomes faster, which finally results relative density and fractured strength of sintered compacts reaching the highest (90.47 % and 77.98 MPa, respectively) in current work. The successfully synthesis of (MgCoNiZnCu)O through ceramic injection molding illustrates this near net shaping process could be a promising route for preparation of high entropy oxides.

Material Efficiency and Economics of Hybrid Additive Manufacturing

In the past few years, Hybrid Additive Manufacturing has emerged to take advantage of both Additive Manufacturing and Subtractive Manufacturing processes and also to overcome the limitation of one process with the other. In aerospace applications, material wastage has become an issue in conventional machining process which reflects in total production cost and time. Especially, when dealing with expensive materials, conventional processes lack material efficiency with high buy-to-fly ratio which results in increased material cost. This paper deals with Hybrid Additive Manufacturing involving two different volume partitioning strategies — (i) Feature-based volume partitioning method (ii) Stock-based near net-shaping volume partitioning method to discuss the economics and material efficiency of Hybrid Additive Manufacturing process via simple cost estimator (formulated from the existing literature) by comparing these two volume partitioning strategies through suitable case studies — (i) Turbine blade and (ii) Impeller. From the results, it was found that the feature-based volume partitioning method was found to be material efficient and cost effective than the stock based near net shaping volume partitioning method in both the case studies.

Near Solidus Forming (NSF): Semi-Solid Steel Forming at High Solid Content to Obtain As-Forged Properties

Near solidus forming (NSF) of steels is a novel process under the umbrella of semi-solid forming technologies midway between classical hot forging and semi-solid technologies. This article presents the work done at Mondragon Unibertsitatea to develop this technology and demonstrates the great potential of the NSF process. The study proves the capability of the process to reduce raw material consumption by 20%, reduce forming loads from 2100 t to 300 t, and reduce forming steps from three to one, to obtain as-forged mechanical properties, as well as the excellent repeatability of the process. The work demonstrates that manufacturing commercial steel components in a single step using several off-the-shelf alloys is possible thanks to the flowing pattern of the material, which enables near-net shaping. In the first part of the article, a general overview of the semi-automated near solidus forming cell, together with a description of the NSF manufacturing trials, is provided, followed by the presentation and discussion of the results for the selected steel alloys.

Laser Deposition-Additive Manufacturing of Graphene Oxide Reinforced IN718 Alloys: Effects on Surface Quality, Microstructure, and Mechanical Properties

Owing to its high stiffness and strength, low density, and excellent flexibility, nano-sized graphene oxide (GO) is considered as a competitive material to reinforce metallic materials. Conventional manufacturing methods for GO reinforced metal matrix fabrication include casting and powder metallurgy, both of which demonstrate disadvantages of high reinforcement agglomeration, high cost, and difficulty in fabrication of complex structures. To reduce these problems, it is important to investigate a finely-controlled, cost-saving, and near-net-shaping process for GO reinforced metal matrix manufacturing. Laser additive manufacturing is such a process that mainly includes selective laser sintering / melting (SLS / M) and laser deposition-additive manufacturing (LD-AM). Compared with SLS / M, LD-AM demonstrates parts remanufacturing capability and is capable of fabricating functionally gradient materials. In this investigation, GO reinforced Inconel 718 (IN718) parts, for the first time, are fabricated using LD-AM processes. The effects of GO on flatness, surface roughness, microstructure, microhardness, and wear resistance of LD-AM fabricated GO reinforced IN718 parts are studied. Experimental results show that the introduction of GO is beneficial for enhancing both microhardness and wear resistance but harmful to surface quality of fabricated parts. In addition, the presence of GO has little influence on microstructures.

Model Predictive Control of the Punch Speed for Damage Reduction in Isothermal Hot Forming

Isothermal forging processes are typically used for near-net shaping of high-performance components such as turbine discs and blades. Recent developments have introduced isothermally forged titanium aluminides into commercial jet engines. Titanium aluminides are lightweight intermetallic compounds with excellent creep properties but very limited ductility. Their low workability requires isothermal forging at slow strain rates, which is typically kept constant in the process. This work explores the possibility of controlling the strain rate during the process using model predictive control, so that the process time is reduced while the microstructure transformation and the amount of damage introduced into the workpiece are controlled. The results of isothermal compression with friction show that both an acceleration of the process and a reduction of damage are possible using the suggested control strategy.

Advanced Waterjet Technology for Machining Curved and Layered Structures

Considerable advancements in waterjet technology take advantage of its inherent merits as a versatile machine tool have been achieved in recent years. Such advancements include, but are not limited to, process automation, machining precision, multimode machining of most materials from macro to micro scales, and cost effectiveness with fast turnaround. In particular, waterjet as a cold cutting tool does not introduce heat-affected zones (HAZ) and preserves the integrity of parent materials. As such, for heat-sensitive materials, its cutting speed is over ten times faster than those of thermal-based tools, such as solid-state lasers, electric discharge machining (EDM), and plasmas cutting. Although waterjet is basically a 2D machined tool, novel multi-axis accessories were developed to enable 3D machining and for machining on workpieces with 3D geometry. For composites, waterjet unlike mechanical routers is capable of minimizing or mitigating tearing and fraying. CNC hard tools that are in direct contact with highly abrasive composite matrix often experience rapid wearing while the heat generated by machining processes induces thermal damage to the composite. This is a nonissue for waterjet as it is a noncontact tool. The only issue for machining composites with waterjet was the damage caused by large stagnating pressure developed inside blind holes during the initial piercing operation (before breakthrough). Considerable effort was made to understand and resolve the waterjet piercing damage issue. For extremely precise parts, waterjet can serve advantageously as a near-net shaping tool; the parts can then be finished by light trimming with proper precision tools. Since the bulk of the material is removed by waterjet, the operating lives of the precision tools can be greatly extended. This paper presents a collection of waterjet-machined samples to demonstrate many benefits by applying waterjet for multimode machining of curved and layered structures.