Materials

Research

Jump to: Review

23 pages, 17078 KiB

Open AccessArticle

Evaluation of Dislocation Densities in Various Microstructures of Additively Manufactured Ti6Al4V (Eli) by the Method of X-ray Diffraction

by Amos Muiruri, Maina Maringa and Willie du Preez

Materials 2020, 13(23), 5355; https://doi.org/10.3390/ma13235355 - 26 Nov 2020

Cited by 44 | Viewed by 3887

Abstract

Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress [...] Read more.

Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

18 pages, 6675 KiB

Open AccessArticle

Characterising the Microstructure of an Additively Built Al-Cu-Li Alloy

by Iris Raffeis, Frank Adjei-Kyeremeh, Uwe Vroomen, Silvia Richter and Andreas Bührig-Polaczek

Materials 2020, 13(22), 5188; https://doi.org/10.3390/ma13225188 - 17 Nov 2020

Cited by 17 | Viewed by 2326

Abstract

Al-Cu-Li alloys are famous for their high strength, ductility and weight-saving properties, and have for many years been the aerospace alloy of choice. Depending on the alloy composition, this multi-phase system may give rise to several phases, including the major strengthening T₁ [...] Read more.

Al-Cu-Li alloys are famous for their high strength, ductility and weight-saving properties, and have for many years been the aerospace alloy of choice. Depending on the alloy composition, this multi-phase system may give rise to several phases, including the major strengthening T₁ (Al₂CuLi) phase. Microstructure investigations have extensively been reported for conventionally processed alloys with little focus on their Additive Manufacturing (AM) characterised microstructures. In this work, the Laser Powder Bed Fusion (LPBF) built microstructures of an AA2099 Al-Cu-Li alloy are characterised in the as-built (no preheating) and preheat-treated (320 °C, 500 °C) conditions using various analytical techniques, including Synchrotron High-Energy X-ray Diffraction (S-HEXRD). The observed dislocations in the AM as-built condition with no detected T₁ precipitates confirm the conventional view of the difficulty of T₁ to nucleate on dislocations without appropriate heat treatments. Two main phases, T₁ (Al₂CuLi) and T_B (Al_7.5Cu₄Li), were detected using S-HEXRD at both preheat-treated temperatures. Higher volume fraction of T₁ measured in the 500 °C (75.2 HV_0.1) sample resulted in a higher microhardness compared to the 320 °C (58.7 HV_0.1) sample. Higher T_B volume fraction measured in the 320 °C sample had a minimal strength effect. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

18 pages, 9327 KiB

Open AccessArticle

Effects of Build Direction on the Mechanical Properties of a Martensitic Stainless Steel Fabricated by Selective Laser Melting

by Ling-Chieh Shen, Xi-Huai Yang, Jeng-Rong Ho, Pi-Cheng Tung and Chih-Kuang Lin

Materials 2020, 13(22), 5142; https://doi.org/10.3390/ma13225142 - 15 Nov 2020

Cited by 17 | Viewed by 2489

Abstract

Mechanical properties and microstructure are investigated for a martensitic stainless steel (AISI 420) fabricated by selective laser melting (SLM) in three build directions. The tensile specimens built by SLM are classified into three groups. Group A is horizontally built in the thickness direction, [...] Read more.

Mechanical properties and microstructure are investigated for a martensitic stainless steel (AISI 420) fabricated by selective laser melting (SLM) in three build directions. The tensile specimens built by SLM are classified into three groups. Group A is horizontally built in the thickness direction, Group B is horizontally built in the width direction, and Group C is vertically built in the length direction. The loading direction in tensile test is parallel to the build direction of Group C, but perpendicular to that of Groups A and B. Experimental results indicate build direction has significant effects on the residual stress, hardness, and tensile properties of SLM builds. Microstructural analyses indicate the as-fabricated SLM AISI 420 builds exhibit elongated cells and acicular structures which are composed of martensite and retained austenite phases growing along the build direction. Such anisotropy in the microstructure leads to anisotropic mechanical properties as Group C specimens (length direction) exhibit greater yield stress, ultimate tensile stress, and elongation than the specimens of Groups A (thickness direction) and B (width direction). The residual compressive stress in the gauge section also contributes to the superior tensile properties of Group C (length direction), as compared to Groups A (thickness direction) and B (width direction), which exhibit residual tensile stress in the gauge section. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Graphical abstract

18 pages, 5898 KiB

Open AccessArticle

Monotonic and Fatigue Behavior of EBM Manufactured Ti-6Al-4V Solid Samples: Experimental, Analytical and Numerical Investigations

by Wiebke Radlof, Christopher Benz, Horst Heyer and Manuela Sander

Materials 2020, 13(20), 4642; https://doi.org/10.3390/ma13204642 - 17 Oct 2020

Cited by 6 | Viewed by 1967

Abstract

The present study aims to carry out an experimental, analytical and numerical investigation of the monotonic and fatigue performance of electron beam melted Ti-6Al-4V structures. Therefore, tensile tests, multiple step tests and strain-life tests were performed on machined EBM Ti-6Al-4V solid samples. An [...] Read more.

The present study aims to carry out an experimental, analytical and numerical investigation of the monotonic and fatigue performance of electron beam melted Ti-6Al-4V structures. Therefore, tensile tests, multiple step tests and strain-life tests were performed on machined EBM Ti-6Al-4V solid samples. An elastic-plastic material model in combination with a numerical damage model was examined according to the experimental tensile tests. Analytical models proposed by Ramberg and Osgood, as well as Coffin and Manson were obtained to describe the cyclic stress-strain curves and strain-life curves, respectively. The fracture surfaces of the tested samples and the influence of different build directions were analyzed. A prediction of the static and fatigue material properties is of particular importance, e.g., for the safe application of additively manufactured load-bearing implant structures. Based on the determined analytical and numerical models, the material and product behavior of complex electron beam melted structures under cyclic loading and fatigue life determination can be investigated in the early stages of the product development process. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

19 pages, 5646 KiB

Open AccessArticle

Thermo-Fluid-Dynamic Modeling of the Melt Pool during Selective Laser Melting for AZ91D Magnesium Alloy

by Hongyao Shen, Jinwen Yan and Xiaomiao Niu

Materials 2020, 13(18), 4157; https://doi.org/10.3390/ma13184157 - 18 Sep 2020

Cited by 20 | Viewed by 2898

Abstract

A three dimensional finite element model (FEM) was established to simulate the temperature distribution, flow activity, and deformation of the melt pool of selective laser melting (SLM) AZ91D magnesium alloy powder. The latent heat in phase transition, Marangoni effect, and the movement of [...] Read more.

A three dimensional finite element model (FEM) was established to simulate the temperature distribution, flow activity, and deformation of the melt pool of selective laser melting (SLM) AZ91D magnesium alloy powder. The latent heat in phase transition, Marangoni effect, and the movement of laser beam power with a Gaussian energy distribution were taken into account. The influence of the applied linear laser power on temperature distribution, flow field, and the melt-pool dimensions and shape, as well as resultant densification activity, was investigated and is discussed in this paper. Large temperature gradients and high cooling rates were observed during the process. A violent flow occurred in the melt pool, and the divergent flow makes the melt pool wider and longer but shallower. With the increase of laser power, the melt pool’s size increases, but the shape becomes longer and narrower. The width of the melt pool in single-scan experiment is acquired, which is in good agreement with the results predicted by the simulation (with error of 1.49%). This FE model provides an intuitive understanding of the complex physical phenomena that occur during SLM process of AZ91D magnesium alloy. It can help to select the optimal parameters to improve the quality of final parts and reduce the cost of experimental research. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

13 pages, 17148 KiB

Open AccessCommunication

Additively Manufactured Al/SiC Cylindrical Structures by Laser Metal Deposition

by Ainhoa Riquelme, Pilar Rodrigo, María Dolores Escalera-Rodríguez and Joaquín Rams

Materials 2020, 13(15), 3331; https://doi.org/10.3390/ma13153331 - 27 Jul 2020

Cited by 7 | Viewed by 2122

Abstract

Preliminary characterization of the microstructure of Al/SiCp composites prepared by Laser Metal Deposition (LMD) was analyzed, and the microhardness and wear behavior of the materials manufactured have been evaluated. It has been determined that the combined effect of the laser speed and power [...] Read more.

Preliminary characterization of the microstructure of Al/SiCp composites prepared by Laser Metal Deposition (LMD) was analyzed, and the microhardness and wear behavior of the materials manufactured have been evaluated. It has been determined that the combined effect of the laser speed and power is decisive for the fabrication process. The microstructure characterization shows that the presence of hygroscopic Al₄C₃ can be avoided by adding Ti to the composite matrix. The wear behavior of the LMD samples and their microhardness have been compared with Powder Metallurgy samples with the same composition. The LMD samples showed higher hardness and wear resistance. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

12 pages, 4015 KiB

Open AccessArticle

A357 Alloy by LPBF for Industry Applications

by Massimo Lorusso, Francesco Trevisan, Flaviana Calignano, Mariangela Lombardi and Diego Manfredi

Materials 2020, 13(7), 1488; https://doi.org/10.3390/ma13071488 - 25 Mar 2020

Cited by 17 | Viewed by 3216

Abstract

The aim of this study is to define the process parameters to build components for industrial applications in A357 alloy by Laser Powder Bed Fusion (LPBF) and to evaluate the effects of post-processing heat treatments on the microstructure and mechanical properties in order [...] Read more.

The aim of this study is to define the process parameters to build components for industrial applications in A357 alloy by Laser Powder Bed Fusion (LPBF) and to evaluate the effects of post-processing heat treatments on the microstructure and mechanical properties in order to obtain the highest hardness and strength. First, process parameters values were defined to obtain full dense components with highest productivity. Then samples were built for microstructural, hardness, and tensile strength investigation in different conditions: as-built, after a stress-relieving treatment, and after a T6 precipitation hardening treatment. For this latest treatment, different time and temperatures for solution and ageing were investigated to find the best in terms of final hardness achievable. It is demonstrated that samples in A357 alloy can be successfully fabricated by LPBF with a density of 99.9% and a mean hardness value achievable of 116 HV0.1, in as-built condition. However, for production purposes, it is fundamental to reduce the residual stresses typical of LPBF. It was shown that a similar hardness value could be obtained after a stress-relieving treatment followed by a proper T6 treatment, together with a coarser but more isotropic microstructure. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

21 pages, 9040 KiB

Open AccessArticle

Damage Tolerance Evaluation of E-PBF-Manufactured Inconel 718 Strut Geometries by Advanced Characterization Techniques

by Daniel Kotzem, Tizian Arold, Thomas Niendorf and Frank Walther

Materials 2020, 13(1), 247; https://doi.org/10.3390/ma13010247 - 06 Jan 2020

Cited by 15 | Viewed by 3267

Abstract

By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile [...] Read more.

By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile or fatigue strength are not sufficient to guarantee safe and reliable use in demanding applications. Within this work, the damage tolerance of E-PBF-manufactured Ni-based alloy Inconel 718 (IN 718) strut geometries under uniaxial cyclic loading was investigated supported by several advanced measurement techniques. Based on thermal and electrical measurements, the failure of single struts could reliably be detected, revealing that continuous monitoring is applicable for such complex geometries. Process-induced surface roughness was found to be the main reason for early failure during cyclic loading. Thus, adequate post-processing steps have to be established for complex geometries to significantly improve damage tolerance and, eventually, in-service properties. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

16 pages, 2596 KiB

Open AccessArticle

High-Performance Nylon-6 Sustainable Filaments for Additive Manufacturing

by Ilenia Farina, Narinder Singh, Francesco Colangelo, Raimondo Luciano, Giulio Bonazzi and Fernando Fraternali

Materials 2019, 12(23), 3955; https://doi.org/10.3390/ma12233955 - 28 Nov 2019

Cited by 40 | Viewed by 5694

Abstract

This study deals with the development of Nylon-6 fused deposition modeling (FDM) filaments for additive manufacturing, which couples high mechanical performances with eco-sustainability. These filaments were extruded from recycled Nylon-6 granulates through a dedicated twin-screw extrusion line, which processes either pure Nylon-6 grains, [...] Read more.

This study deals with the development of Nylon-6 fused deposition modeling (FDM) filaments for additive manufacturing, which couples high mechanical performances with eco-sustainability. These filaments were extruded from recycled Nylon-6 granulates through a dedicated twin-screw extrusion line, which processes either pure Nylon-6 grains, or mixtures of such a material with minor fractions of acrylonitrile butadiene styrene (ABS) and titanium dioxide (TiO₂). The rheological and thermal properties of the investigated filaments are analyzed, including melt flow index, melting temperature, and decomposition temperature, which are of the utmost importance when avoiding the overheating and decomposition of the material. Such a study is conducted in both pre-extrusion and post-extrusion conditions. The tensile strength, the wear resistance, and the printability of the examined recycled Nylon-6 filaments are also studied by comparing the properties of such filaments with those exhibited by different nylon-based filaments for FDM that are available in the market. The given results show that the recycling of Nylon-6 through the “caprolactam” regeneration route enables the newly formed material to retain high physical and mechanical properties, such as tensile strength at yield in the interval 55.79–86.91 MPa. Referring to the basic composition of the filaments examined in the present study, this remarkably high-yield strength is accompanied by a Young modulus of 1.64 GPa, and wear resistance of 92 µm, under a 15 min/1 kg load pin-on-disk test carried at the sliding speed of 250 rpm. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

10 pages, 7116 KiB

Open AccessArticle

Mechanical and Microstructural Characterization of Arc-Welded Inconel 625 Alloy

by Daniel Kotzem, Lucas Beermann, Mustafa Awd and Frank Walther

Materials 2019, 12(22), 3690; https://doi.org/10.3390/ma12223690 - 08 Nov 2019

Cited by 6 | Viewed by 2583

Abstract

The objective of this work was to verify a relatively new fusion-based additive manufacturing (AM) process to produce a high-temperature aerospace material. The nickel-based superalloy Inconel 625 (IN625) was manufactured by an arc-based AM technique. Regarding microstructure, typical columnar-oriented dendritic structure along the [...] Read more.

The objective of this work was to verify a relatively new fusion-based additive manufacturing (AM) process to produce a high-temperature aerospace material. The nickel-based superalloy Inconel 625 (IN625) was manufactured by an arc-based AM technique. Regarding microstructure, typical columnar-oriented dendritic structure along the building direction was present, and epitaxial growth was visible. The mechanical behavior was characterized by a combination of quasi-static tensile and compression tests, whereas IN625 showed high yield and ultimate tensile strength with a maximum fracture strain of almost 68%. Even quasi-static compression tests at room and elevated temperatures (650 °C) showed that compression strength only slightly decreased with increasing temperature, demonstrating the good high-temperature properties of IN625 and opening new possibilities for the implementation of arc-based IN625 in future industrial applications. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Figure 1

Review

Jump to: Research

23 pages, 2220 KiB

Open AccessReview

Implementing FDM 3D Printing Strategies Using Natural Fibers to Produce Biomass Composite

by Waleed Ahmed, Fady Alnajjar, Essam Zaneldin, Ali H. Al-Marzouqi, Munkhjargal Gochoo and Sumayya Khalid

Materials 2020, 13(18), 4065; https://doi.org/10.3390/ma13184065 - 13 Sep 2020

Cited by 66 | Viewed by 7613

Abstract

Current environmental concerns have led to a search of more environmentally friendly manufacturing methods; thus, natural fibers have gained attention in the 3D printing industry to be used as bio-filters along with thermoplastics. The utilization of natural fibers is very convenient as they [...] Read more.

Current environmental concerns have led to a search of more environmentally friendly manufacturing methods; thus, natural fibers have gained attention in the 3D printing industry to be used as bio-filters along with thermoplastics. The utilization of natural fibers is very convenient as they are easily available, cost-effective, eco-friendly, and biodegradable. Using natural fibers rather than synthetic fibers in the production of the 3D printing filaments will reduce gas emissions associated with the production of the synthetic fibers that would add to the current pollution problem. As a matter of fact, natural fibers have a reinforcing effect on plastics. This review analyzes how the properties of the different polymers vary when natural fibers processed to produce filaments for 3D Printing are added. The results of using natural fibers for 3D Printing are presented in this study and appeared to be satisfactory, while a few studies have reported some issues. Full article

(This article belongs to the Special Issue Characterization and Properties of Materials Produced by Additive Manufacturing)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Characterization and Properties of Materials Produced by Additive Manufacturing

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Related Special Issue

Published Papers (11 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI