Grain selection and growth orientation of prior-β phase for Ti-6-4 during additive manufacturing:insights from a modeling perspective

The microstructure of Ti-6-4 components produced by additive manufacturing suffers from the coarse and elongated prior-β grain,which leads to a decrease of the tensile behavior and the occurrence of anisotropy.To understand and control the grain evolution,a multiscale simulation is applied to investigate the relationship between the grain selection,growth orientation,and the molten pool morphology with the different deposition layer numbers and processing parameters.The accuracy of the simulation is validated by experiments in both qualitative and quantitative ways.Results show that when the grain with unfavorable orientation loses the competitive growth with its neighbors,there will be a great chance that the blocked grain is eliminated in the following layer-and-layer deposition,which leads to the increase of the grain width.The size of the molten pool increases remarkably as the layer number increases,which lays a heavy burden on the stability of the molten pool.The analytical relationship between the molten pool morphology and the grain growth orientation is also deduced.The flat molten pool causes the grains with the <001> direction close to the building direction to have greater survival potential.Besides,decreasing the line power energy shows little effect on the stability of the molten pool and the grain growth orientation,especially when the deposited layer number is large.The revealing mechanisms will help in understanding and further controlling the grain evolution.

Analyzing the Interplay of Sintering Conditions on Microstructure and Hardness in Indirect Additive Manufacturing of 17-4PH Stainless Steel

Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusion additive manufacturing(ADAM),a variant of indirect AM methods,is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding.However,there is still limited knowledge of the process conditions and material properties fabricated through this process,where sintering plays a crucial role in the final consolidation of parts.Therefore,this research,for the first time,systematically investigates the impact of various sintering conditions on the shrinkage,relative density,microstructure,and hardness of the 17-4PH ADAM samples.For this reason,as-washed samples were sintered under different time-temperature combinations.The sample density was evaluated using Archimedes,computed tomography,and image analysis methods.The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples.The results indicated more than 99% relative densities,higher than the value reported by Markforged Inc.(~96%).Based on parallel porosities observed in the computed tomography results,it can be suggested that by modifying the infill pattern during printing,it would be possible to increase the final relative density.The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc.Sintering at 1330℃ for 4 h increased the density of the printed sample without compromising its mechanical properties.According to X-ray diffraction analysis,the standard sample provided by Markforged Inc.and“1330℃—4 h”one had similar stable phases,although copper-rich intermetallics were more abundant in the microstructure of reference samples.This study is expected to facilitate the adoption of indirect metal AM methods by different sectors,thanks to the high achievable relative densities reported here.

The effects of fabrication atmosphere condition on the microstructural and mechanical properties of laser direct manufactured stainless steel 17-4 PH

The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through mea-surements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition pos-sessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.

Homogenization on solution treatment and its effects on the precipitation-hardening of selective laser melted 17-4PH stainless steel

17-4 precipitation-hardened(PH)stainless steel(SS)exhibits high strength and good corrosion resistance via Cu-precipitation hardening.Unlike conventional wrought 17-4PH SS,Cu segregation andε-Cu pre-cipitates are observed in additively manufactured(AM)17-4PH SS owing to the repeated rapid cooling after heating,which characterizes the AM process.In this study,solution treatment was conducted under various temperatures(1,000,1,050,1,100,and 1,200℃)and durations(1,2,4,and 8 h)to minimize the negative effects of Cu segregation andε-Cu precipitates on precipitation hardening.The mechanical prop-erties and microstructures of each condition for the Cu precipitation behavior were examined.Although theε-Cu precipitates did not disappear after solution treatment,the average diameter of theε-Cu precipi-tates tended to decrease with increasing solution treatment temperature and duration.Therefore,solution treatment at a temperature of 1,200℃ for 8 h was the best,resulting in improved strength compared to the conventional solution treatment at 1,050℃.Solution treatment on at least 1,100℃ is effective in AM.

Tandem rapid manufacturing of Inconel-625 using laser assisted and plasma transferred arc depositions

This paper presents an investigation on depo- sition of Inconel-625 using laser rapid manufacturing （LRM） and plasma transferred arc （PTA） deposition in individual and tandem mode. LRM has advantages in terms of dimensional accuracy, improved mechanical properties, finer process control, reduced heat input and lower thermal distortion, while PTA scores more in terms of lower initial investment, lower running cost and higher deposition rate. To quantify the clubbed advantages and limitations of both processes, these were studied individually and in tandem. A number of samples were deposited at different process parameters like power, scan speed, powder feed rate. They were subjected to tensile test, adhesion-cohesion test, impact test and micro hardness measurement. The results of individual tests showed the comparable mechanical prop- erties with i20% variation. The mixed dendritic-cellular and dendritic-columnar microstructures were respectively observed for LRM and PTA deposits with a distinct inter- face for the case of tandem deposition. The interface strength of tandem deposits was evaluated employing adhesion-cohesion test, and it was found to be （325 i 35） MPa. The study confirmed the viability of LRM and PTA deposition in tandem for hybrid manufacturing.

A holistic decision support tool for remanufacturing： end-of-life （EOL） strategy planning

Remanufacturing is a key enabler for sustainable production due to its effectiveness in closing the loop on material flows, extending product life cycle and reducing production waste and emission. In this paper, a holistic decision support tool to facilitate the product end-of-life （EOL） strategy planning, specifically using remanufactur- ing as a key strategy is presented. The proposed model incorporates checklist methods to evaluate the viability of conducting remanufactufing for a product and its compo- nents. An optimization model for determining the Pareto set of optimal EOL strategies that correspond to maximum economic profit and minimum environmental impact is presented. Since determination of this Pareto set via enu- meration of all EOL strategies is prohibitively time-con- suming, even for a product with a small number of components, genetic algorithm （GA）, specifically NSGA-II has been utilized to achieve rapid calculation of the set of optimum EOL strategies. This NSGA-II method permits extensive sensitivity analysis to understand thoroughly the impact of situational variables, such as reverse logistic cost, technology and replacement part availability, etc., on the EOL decision making, i.e., Pareto front, and thus leading to improved strategy planning and better product design. The case study involving EOL treatment of two types of desktop phones is described to illustrate the utility of the proposed methodology.

On the microstructure and texture evolution in 17-4 PH stainless steel during laser powder bed fusion: Towards textural design

Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless steel is a high strength, high corrosion resistance alloy used in a range of industries suitable forAM, such as aerospace and marine. Despite 17-4 PH being one of the most common steels for AM, thereare still gaps in the understanding of its AM processing–structure relationships. These include the natureof the matrix phase, as well as the development of texture through AM builds under different processingconditions. We have investigated how changing the laser power and scanning strategy affects the microstructure of 17-4 PH during laser powder bed fusion. It is revealed that the matrix phase is δ-ferritewith a limited austenite presence, mainly in regions of the microstructure immediately below melt pools.Austenite fraction is independent of the printing pattern and laser power. However, reducing the timebetween adjacent laser passes during printing results in an increase in the austenite volume fraction.Another effect of the higher laser power, as well as additional remelting within the printing strategy, isan increase in the average grain size by epitaxial ferrite grain growth across multiple build layers andthe development of a mosaic type microstructure. Changes to the scanning strategy have significant impacts on the textures observed along the build direction, while (100) texture along the scanning directionis observed consistently. Mechanisms for texture formation and the mosaic structure are proposed thatpresents a pathway to the design of texture via AM process control.

A differentiated approach for justification of advanced manufacturing technologies

European companies rely on advanced manu- facturing technologies （AMTs） in order to succeed in an environment of high labour costs, increasing competition and rising customer expectations. AMT implementation is often a high-risk investment. Many companies experience a misalignment between the installed functionality and pro- duction needs. There is a need for decision support in order to take into account all possible advantages and disad- vantages of the technology implementation, and ensure that the technology meets the requirements of the production processes. In this article, a differentiated technology justi- fication approach is introduced. The approach suggests a combination of strategic, financial and risk justification methods. The recommended number and type of methods depend on the integration level of the technical system under consideration, ranging from stand-alone machines to large and integrated production systems. The approach was developed based on a literature review and a case study. The application of the approach was presented in a case where several types of pipe bending technology were evaluated.

Logistics Network Design for Manufacturing Enterprises with Component Processing Workshops

Logistics network design influences the efficiency and cost of Logistics directly.Some manufacturing enterprises not only have warehouse hubs,but also build component processing workshops which are usually located in those places where the costs of materials and workforce are lower.This paper establishes a logistics network design model for the manufacturing enterprises with component processing workshops based on 0-1 mixture integer programming.The model optimizes the logistics network in an integrated view,by which the selection of the nodes,the manufacturing plan,and transportation plan can be obtained.An example is given to verify its feasibility.The approach is helpful for designing of the logistics network in manufacturing enterprises.

Current status,enablers&barriers of implementing cellular manufacturing system in Indian industries

The cellular manufacturing （CM） has been proved as a well-known manufacturing strategy that helps to improve manufacturing efficiency and productivity by utilizing the philosophy of group technology. Large num- ber of papers has been published in the area of design issues of CM system. Unfortunately, the issues related to acceptability of CM in Indian industries are typically not examined rigorously as technical issues. This paper pre- sents the results of a survey carded out to find the status, enabler and barrier of implementing CM system in Indian industries.

Metallurgical concepts for optimized processing and properties of carburizing steel

Carburized steel grades are widely used in applications where high surface near hardness is required in combination with good core toughness as well as high strength and fatigue resistance. The process of carburizing lower to medium carbon containing steel can generally provide this combination of properties and has been prac- ticed for several decades. Such steel is essential in the vehicle power-train, machines and power generation equipment. However, the increasing performance demands by such applications as well as economical considerations forced steel producers to develop better alloys and fabri- cators to design more efficient manufacturing processes. The present paper describes recent concepts for alloy design optimization of carburizing steel and demonstrates the forthcoming beneficial consequences with regard to manufacturing processes and final properties.