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Microstructure and Mechanical Properties of Laser Additive Manufactured Metals

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (31 August 2021) | Viewed by 12314

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Prof. Dr. Mariangela Lombardi

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1. Integrated Additive Manufacturing Center (IAM)—Politecnico di Torino, Corso Castelfidardo, 51, 10129 Torino, Italy
2. Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca Degli Abruzzi, 24, 10129 Torino, Italy
Interests: laser powder bed fusion; directed energy deposition; aluminum alloys; microstructures; mechanical properties
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Dear Colleagues,

Nowadays, only a limited number of commercial alloy systems can be processed through Laser Additive Manufacturing technologies, such as Laser Powder Bed Fusion or Directed Energy Deposition. In particular, additive manufactured titanium alloys, stainless steels, nickel-based superalloys, Al-Si alloys, cobalt chromium and recently high-entropy alloys have already been developed. At the same time, developing new alloy compositions is now becoming a key challenge to address in the additive manufacturing field.

Finding the right window for the main process parameters and the conditions of the thermal treatments is a core procedure for reaching interesting mechanical performances for additive manufactured metals. On the basis of the powder characteristics, the machine, and the conditions fixed for processing and post-processing, different compositions and microstructures can be obtained, and, consequently, metallic parts with different mechanical properties can be produced.

The knowledge of the relations among processing and post-processing conditions, compositions, and microstructures of additive manufactured materials and mechanical features of metallic parts is fundamental for contributing to the diffusion and the evolution of laser additive manufacturing technologies.

This Special Issue aims to present the latest research related to the study of metals processed through laser additive manufacturing technologies, from process parameter definition to thermal treatment optimization focusing the attention on microstructural and mechanical characteristics of the processed materials. Reviews focused on innovations on metals for laser additive manufacturing are also welcome.

Prof. Mariangela Lombardi
Guest Editor

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Keywords

laser powder bed fusion
directed energy deposition
new alloys for additive manufacturing
microstructures
mechanical behavior

Published Papers (5 papers)

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Research

20 pages, 8842 KiB

Open AccessArticle

Selective Laser Melting of Stainless Steel 316L with Face-Centered-Cubic-Based Lattice Structures to Produce Rib Implants

by Cho-Pei Jiang, Alvian Toto Wibisono and Tim Pasang

Materials 2021, 14(20), 5962; https://doi.org/10.3390/ma14205962 - 11 Oct 2021

Cited by 10 | Viewed by 3044

Abstract

Selective laser melting has a great potential to manufacture biocompatible metal alloy scaffolds or implants with a regulated porosity structure. This study uses five face-centered cubic (FCC) lattice structures, including FCC, FCC-Z, S-FCC, S-FCC-Z, and FCC-XYZ. Specimens with different lattice structures are fabricated using two laser energy densities, 71 J/mm³ and 125 J/mm³. Density, tensile, compressive and flexural test results exhibit the effect of laser parameters and lattice structure geometries on mechanical properties. The higher laser energy density of 125 J/mm³ results in higher properties such as density, strength, and Young’s modulus than the laser energy density of 71 J/mm³. The S-FCC lattice has the lowest density among all lattices. The mechanical tests result show specimen with FCC-XYZ lattice structures fabricated using a laser energy density of 125 J/mm³ meet the tensile properties requirement for human ribs. This structure also meets the requirement in flexural strength performance, but its stiffness is over that of human ribs. The compression test results of lattices are still incomparable due to unavailable compression data of the human ribs. In short, The FCC-XYZ lattice design fabricated by the 125 J/mm³ laser energy density parameter can be used to manufacture customized rib implants. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Laser Additive Manufactured Metals)

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11 pages, 4508 KiB

Open AccessArticle

Microstructural Tailoring and Enhancement in Compressive Properties of Additive Manufactured Ti-6Al-4V Alloy through Heat Treatment

by Byungmin Ahn

Materials 2021, 14(19), 5524; https://doi.org/10.3390/ma14195524 - 24 Sep 2021

Cited by 7 | Viewed by 1909

Abstract

Among laser additive manufacturing, selective laser melting (SLM) is one of the most popular methods to produce 3D printing products. The SLM process creates a product by selectively dissolving a layer of powder. However, due to the layerwise printing of metal powders, the initial microstructure is fully acicular α′-martensitic, and mechanical properties of the resultant product are often compromised. In this study, Ti-6Al-4V alloy was prepared using SLM method. The effect of heat treatment was carried out on as-built SLM Ti-6Al-4V alloy from 650–1000 °C to study respective changes in the morphology of α/α′-martensite and mechanical properties. The phase transition temperature was also analyzed through differential thermal analysis (DTA), and the microstructural studies were undertaken by optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties were assessed by microhardness and compressive tests before and after heat treatment. The results showed that heat treated samples resulted in a reduction in interior defects and pores and turned the morphology of the α′-martensite into a lamellar (α + β) structure. The strength was significantly reduced after heat treatment, but the elongation was improved due to the reduction in columnar α′-martensite phase. An optimum set of strength and elongation was found at 900 °C. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Laser Additive Manufactured Metals)

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13 pages, 7599 KiB

Open AccessArticle

An Automatic on Top Analysis of Single Scan Tracks to Evaluate the Laser Powder Bed Fusion Building Parameters

by Alessandra Martucci, Fabrizio Marinucci, Antonio Sivo, Alberta Aversa, Diego Manfredi, Federica Bondioli, Paolo Fino and Mariangela Lombardi

Materials 2021, 14(18), 5171; https://doi.org/10.3390/ma14185171 - 9 Sep 2021

Cited by 4 | Viewed by 1507

Abstract

The production of dense samples produced by laser powder bed fusion (LPBF) is mainly determined by the choice of the best combination of construction parameters. Parameter optimization is the first step in the definition of an LPBF process for new alloys or systems. With this goal, much research uses the single scan track (SST) approach for a preliminary parameter screening. This study investigates the definition of a computer-aided method by using an automatic on top analysis for the characterization of SSTs, with the aim of finding ranges of laser power and scan speed values for massive production. An innovative algorithm was implemented to discard non-continuous scans and to measure the SSTs quality using three regularity indexes. Only open source software were used to fine tune this approach. The obtained results on Al4Cu and AlSi10Mg realized with two different commercial systems suggest that it is possible to use this method to easily narrow the process parameter window that allows the production of dense samples. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Laser Additive Manufactured Metals)

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14 pages, 52729 KiB

Open AccessArticle

Base Plate Preheating Effect on Microstructure of 316L Stainless Steel Single Track Deposition by Directed Energy Deposition

by Abhilash Kiran, Martina Koukolíková, Jaroslav Vavřík, Miroslav Urbánek and Jan Džugan

Materials 2021, 14(18), 5129; https://doi.org/10.3390/ma14185129 - 7 Sep 2021

Cited by 12 | Viewed by 2968

Abstract

The microstructural morphology in additive manufacturing (AM) has a significant influence on the building structure. High-energy concentric heat source scanning leads to rapid heating and cooling during material deposition. This results in a unique microstructure. The size and morphology of the microstructure have a strong directionality, which depends on laser power, scanning rate, melt pool fluid dynamics, and material thermal properties, etc. The grain structure significantly affects its resistance to solidification cracking and mechanical properties. Microstructure control is challenging for AM considering multiple process parameters. A preheating base plate has a significant influence on residual stress, defect-free AM structure, and it also minimizes thermal mismatch during the deposition. In the present work, a simple single track deposition experiment was designed to analyze base plate preheating on microstructure. The microstructural evolution at different preheating temperatures was studied in detail, keeping process parameters constant. The base plate was heated uniformly from an external heating source and set the stable desired temperature on the surface of the base plate before deposition. A single track was deposited on the base plate at room temperature and preheating temperatures of 200 °C, 300 °C, 400 °C, and 500 °C. Subsequently, the resulting microstructural morphologies were analyzed and compared. The microstructure was evaluated using electron backscattered diffraction (EBSD) imaging in the transverse and longitudinal sections. An increase in grain size area fraction was observed as the preheating temperature increased. Base plate preheating did not show influence on grain boundary misorientation. An increase in the deposition depth was noticed for higher base plate preheating temperatures. The results were convincing that grain morphology and columnar grain orientation can be tailored by base plate preheating. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Laser Additive Manufactured Metals)

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14 pages, 7525 KiB

Open AccessArticle

Study on the Effect of Ni Addition on the Microstructure and Properties of NiTi Alloy Coating on AISI 316 L Prepared by Laser Cladding

by Yuqiang Feng, Zexu Du and Zhengfei Hu

Materials 2021, 14(16), 4373; https://doi.org/10.3390/ma14164373 - 4 Aug 2021

Cited by 8 | Viewed by 1845

Abstract

This paper investigated 55 NiTi commercial alloy powder and 55 NiTi with 5% pure Ni mixed powder (55 NiTi + 5 Ni) coatings fabricated by laser cladding to study the effect of extra Ni addition on the microstructure and properties of the coating. The XRD and EDS results show that the major phases in the coatings were NiTi and Ni₃Ti. Besides that, a second phase like Ni₄Ti₃, Fe₂Ti, and NiTi₂ was also detected, among which, NiTi₂ was only found in 55 NiTi coating. The proportion of the phase composition in the coating was calculated via the software Image-Pro Plus. The hardness of the cladding layer reaches 770–830 HV, which was almost four times harder than the substrate, and the hardness of 55 NiTi + 5 Ni coating was around 8% higher than that of 55 NiTi coating. The wear resistance of the 55 NiTi + 5 Ni coating was also better; the wear mass loss decreased by about 13% and with a smaller friction coefficient compared with the 55 NiTi coating. These results are attributed to the solid solution strengthening effect caused by Ni addition and the second phase strengthening effect caused by the content increase of the Ni₃Ti phase in the cladding layer. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Laser Additive Manufactured Metals)

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