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Additive manufacturing (AM) of metals has gained massive attention due to its salient features, such as a tool-free process, near-net shape product development, less fabrication time, and no restriction on product size. This paper provides a brief overview of common metal AM processes, including powder bed fusion, binder jetting, directed energy deposition, and sheet lamination. The advantages of each metal AM technology and their limitations are compared and addressed with examples. Critical steps to ensure the successful 3D printing of metal structures are discussed for each metal AM approach. The effect of each processing parameter is critically analyzed to enhance fabrication characteristics. The metal AM mechanisms, optimization of processing parameters, powder preparation techniques and their effects on the powder morphology, and applications of metal AM are discussed.

• Coarse non-spherical powder locally decreases cooling rates during laser powder bed fusion. • Locally lower cooling rates results in β/β grain boundary α variant selection. • Self-accommodation was the main variant selection mechanism. • Type 4 was the dominant α/α grain boundary variant. • Category II variant cluster was analytically proved to be dominant. The presence of α / α′ on prior β / β grain boundaries directly impacts the final mechanical properties of the titanium alloys. The β / β grain boundary variant selection of titanium alloys has been assumed to be unlikely owing to the high cooling rates in laser powder bed fusion (L-PBF). However, we hypothesize that powder characteristics such as morphology (non-spherical) and particle size (50–120 µm) could affect the initial variant selection in L-PBF processed Ti-6Al-4V alloy by locally altering the cooling rates. Despite the high cooling rate found in L-PBF, results showed the presence of β / β grain boundary α′ lath growth inside two adjacent prior β grains. Electron backscatter diffraction micrographs confirmed the presence of β / β grain boundary variant selection, and synchrotron X-ray high-speed imaging observation revealed the role of the " shadowing effect " on the locally decreased cooling rate because of keyhole depth reduction and the consequent β / β grain boundary α′ lath growth. The self-accommodation mechanism was the main variant selection driving force, and the most abundant α / α boundary variant was type 4 (63.26°//[ 10 ¯ 5 5 3 ¯ ]). The dominance of Category II α lath clusters associated with the type 4 α / α boundary variant was validated using the phenomenological theory of martensite transformations and analytical calculations, from which the stress needed for the β → α′ transformation was calculated. [Display omitted] [ABSTRACT FROM AUTHOR]

ABSTRACTDespite numerous studies on lead-free solder in recent years, only a limited number of publication is available on high temperature lead-free alternative solders to replace high lead solders. Therefore, this research focused on several candidate alloys (Bi-1.5–2.5-3.5 wt.% Ag) as alternative solders for high temperature application. Candidates of Bi-Ag alloys were aged at 160°C for 0, 100, 200, 350 and 500 hours. Morphological characteristics such as grain growth, wetting angle and Cu rich particles size distribution in solder bulk were investigated. The results show that physical and mechanical adhesion between Cu substrate and solder bulk occurred in all three percentages of Ag during isothermal ageing process. In the case of Cu-rich particle size analyses, by increasing the percentages of Ag in the solder alloys, the average size of Cu- rich phase increased. The average measurement of mechanical grain boundary grooving thickness and cross-sectional wetting angle also increased with addition of Ag percentage. However, the value for cross-sectional wetting angle analysis reduce with increasing ageing time. From this work, Bi-2.5 wt% Ag have been identified as the best candidate between the three solders to be explored for future analysis such as mechanical strength data collection and electrical conductivity test.

ABSTRACTDirect tension indicators (DTIs) are one alternative method that is commonly used to verify that high-strength bolts have been properly tensioned during installation. This paper investigates collapse mechanisms and crushing load during the axial compression of the DTI washer. An experimental technique is used to evaluate the function of the DTI washer under compressive quasi-static strain rate. A numerical model is presented based on finite element analysis to simulate crushing of DTI washer considering nonlinear responses due to material behaviour, contact boundary conditions and large deformations. The predicted numerical crushing load and collapse pattern were found to be in good agreement with the experimental results. Finally, the effect of the geometry parameters of the DTI washer on crushing loads is investigated. This study provides practical information about using the DTI washers to confirm proper pre-tensioning of bolts in structural steel fasteners industry.

This study investigates the multifaceted interdependencies among powder characteristics (i.e., non-spherical morphology and particle size ranging 50-120 or 75-175µm), laser powder bed fusion (L-PBF) process condition (i.e., contouring), post-process treatments (i.e., hot isostatic pressing (HIP) and mechanical grinding) on the pore, microstructure, surface finish, and fatigue behavior of additively manufactured Ti-6Al-4V samples. Microstructure analysis shows a phase transformation α′ → α+β microstructure after HIP treatment (at 899±14 °C for 2h under the applied pressure of 1034±34bar) of the as-built Ti-6Al-4V parts. The findings from pore analysis using micro-computed tomography (μ-CT) show an increase in sub-surface pores when relatively smaller powders are L-PBF processed including contouring. Surface optical profilometry reveals a decrease in surface roughness when fine powder is L-PBF including contouring. Pore analysis conducted through μ-CT reveals that the presence of lack-of-fusion pores within the L-PBF processed coarse powder is more pronounced when compared to the fine powder. Furthermore, HIP treatment does not eliminate these pores. The fracture failure in as-printed parts occurs at the surface, while the combination of HIP and mechanical grinding alters crack initiation to subsurface pore defects. Fractography reveals that HIP and as-built samples followed the facet formation and pseudo-brittle fracture mechanisms, respectively. Fatigue life assessments, supported by statistical analysis, indicate that mechanical grinding and HIP significantly enhanced fatigue resistance, approaching the benchmarks set by wrought Ti-6Al-4V alloy. A fatigue prediction model which considers the surface roughness as a micro-notch has been used.

Objectives: Alzheimer's disease (AD) is one of the most common forms of neurodegenerative diseases. Despite vast ongoing researches focusing on the area, little is known about novel treatments. In this study, we aimed to survey the effects of Capparis spinosa(C. spinosa) extract on amyloid-beta peptide (Aβ)-injected rat.Methods: For this purpose, hydroalcoholic extracts of caper leaf and fruit were prepared. Total phenolic content, DPPH, and FRAP assay were accomplished to determine antioxidant activity of C. spinosa. HPLC analysis was conducted to measure rutin and quercetin content of selected parts of the plant. Higher levels of flavonoids were observed in leaves of the plant. Twelve male Wistar Aβ-induced rats were randomly divided in four groups of (1) Aβ−/DW+: Sham-operated group (2) Aβ+/DW+: Aβ-injected group (3) Aβ+/RU+: Standard rutin treatment (4) Aβ+/CS+: C. spinosaextract treatment. After 6 weeks of oral administration, real-time qPCR were conducted to determine APP, BACE-1, PSEN-1, and PSEN-2genes expression in the hippocampus of rats.Results: HPLC analysis showed high levels of rutin and quercetin in leaves of Capparis. Rutin was 16939.2 ± 0.01 and quercetin was 908.93 ± 0.01 µg/g fresh weight. In fruit, 1019.52 ± 0.01 rutin and 97.86 ± 0.01 µg/g FW quercetin were measured. Expression of BACE-1, APP, PSEN-1, and PSEN-2genes in comparison with the control group showed significant down regulation.Discussion: Results of the study demonstrated that C. spinosahas the potential to down regulate inflammation-involved genes in AD, due to its high levels of flavonoids and could be beneficial as a dietary complement in AD patients.

In additively manufactured (AM) metallic materials, the fundamental interrelationships that exist between composition, processing, and microstructure govern these materials’ properties and potential improvements or reductions in performance. For example, by using AM, it is possible to achieve highly desirable microstructural features (e.g., highly refined precipitates) that could not otherwise be achieved by using conventional approaches. Simultaneously, opportunities exist to manage macro-level microstructural characteristics such as residual stress, porosity, and texture, the last of which might be desirable. To predictably realize optimal microstructures, it is necessary to establish a framework that integrates processing variables, alloy composition, and the resulting microstructure. Although such a framework is largely lacking for AM metallic materials, the basic scientific components of the framework exist in literature. This review considers these key components and presents them in a manner that highlights key interdependencies that would form an integrated framework to engineer microstructures using AM.

Mechanical properties of additively manufactured parts are sensitive to the presence of pores form during the manufacturing process. The impact of pores on the mechanical performance has been investigated extensively with respect to different parameters, such as pore volume fraction, shape, and size. However, statistical investigations focusing on the relationships between the spatial distribution of pores and process parameters; and consequently, the performance of the manufactured parts are scattered and limited. Also, these sparse investigations usually suffer from an ambiguous definition of terminologies. For instance, the required criteria to consider a point pattern as complete spatial randomness (CSR) are generally not clarified. Moreover, no numerical formalism is yet developed to show how much the observed spatial results are statistically significant. To address these shortcomings, the statistical definition of CSR in a point pattern and the procedure to quantitatively determine the deviation of a pattern from CSR were discussed. The explained statistical approach was used to investigate the effect of scanning speed parameter on the spatial distribution of gas pores in laser powder bed fusion manufactured stainless steel parts. Furthermore, and to highlight the impact of the spatial distribution of pores on mechanical properties, fatigue performances of parts with clustered and randomly distributed pores were simulated by finite element analysis. It is shown that by reducing the scanning speed, the spatial distribution of gas pores deviated more from CSR, and correspondingly fatigue performance deteriorated.