Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

Laser additive manufacturing of metallic components: materials, processes and mechanisms

Review of in-situ process monitoring and in-situ metrology for metal additive manufacturing

The mechanical behavior, and thus ‘trustworthiness’/durability, of engineering components fabricated via laser-based additive manufacturing (LBAM) is still not well understood. This is adversely affecting the continual adoption of LBAM for part fabrication/repair within the global industry at large. Hence, it is important to determine the mechanical properties of parts fabricated via LBAM as to predict their performance while in service. This article is part of two-part series that provides an overview of Direct Laser Deposition (DLD) for additive manufacturing (AM) of functional parts. The first part (Part I) provides a general overview of the thermo-fluid physics inherent to the DLD process. The objective of this current article (Part II) is to provide an overview of the mechanical characteristics and behavior of metallic parts fabricated via DLD, while also discussing methods to optimize and control the DLD process. Topics to be discussed include part microstructure, tensile properties, fatigue behavior and residual stress – specifically with their relation to DLD and post-DLD process parameters (e.g. heat treatment, machining). Methods for controlling/optimizing the DLD process for targeted part design will be discussed – with an emphasis on monitored part temperature and/or melt pool morphology. Some future challenges for advancing the knowledge in AM-part adoption are discussed. Despite various research efforts into DLD characteristics and process optimization, it is clear that there are still many areas that require further investigation.

An overview of Direct Laser Deposition for additive manufacturing; Part II: Mechanical behavior, process parameter optimization and control

Characterization of stainless steel parts by Laser Metal Deposition Shaping

Selective laser melting (SLM) and laser cladding deposition (LCD) are two typical kinds of laser additive manufacturing techniques that have been developed for many years independently. Although they are based on the same principle of laser cladding, there are little comparison on the fundamental studies for metallurgical behavior (including melting and solidification behaviors) and the mechanical properties of these two techniques up to now. In this paper, the single-track formation and the deposition of block sample from 316L stainless steel powders have been carried out by both SLM and LCD techniques. A comparison on pool shape, cooling rate, columnar grain size and mechanical properties under different processing conditions by LCD and SLM respectively has been studied. It is found that, due to the increase of energy input and the decrease of depth-to-width ratio of melting pool (MP) from SLM to LCD, the primary cellular arm spacing (PCAS) of the sample increases from less than 1.0 µm to more than 15.0 µm, and thus the cooling rate of MP decreases from about 106 K/s in SLM to about 102 K/s in LCD. Furthermore, due to the decrease of cooling rate from SLM to LCD, the columnar grains of the as forming alloy are getting coarser. Especially, the relationship between gain size (λ) and the reciprocal of square root of cooling rate ( T ) in LCD significantly meets the classical linear function of λ = a + b / T (a and b are constants), while a new relationship of a cubic function is found in SLM, showing the different solidification characteristics between LCD and SLM. Lastly, the samples of 316L stainless steel by SLM have much stronger tensile strength but lower elongation than those by LCD, and the main reason is due to that the solidification behavior of the MPs by SLM can form much finer columnar grains than those by LCD.

A comparison on metallurgical behaviors of 316L stainless steel by selective laser melting and laser cladding deposition

First-principles study of the relaxation and energy of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces

Present work applied a kind of new deposition pattern, fractal deposition pattern, in the LSF process. The influences of different depositing patterns (fractal, offset and raster) on the parts’ deformation, interior quality and mechanical properties are also investigated. The finite element method (FEM) simulation results show that the offsetout (the offset from the outside to the inside) and fractal deposition patterns generate the temperature distribution with the circular and eccentric circle symmetry at the end of deposition process, respectively. There are smaller temperature gradients using these two kinds of deposition patterns than those by the raster and offsetin (the offset from the inside to the outside) deposition patterns. It is also found that the magnitude of the transient temperature gradient has a critical effect on part distortion during LSF process. The fractal deposition pattern generates the smallest parts’ deformation, followed by offsetout. The parts interior quality investigation with fractal and offsetout deposition patterns shows that the overlap should be increased to 50% to avoid pore defects. Moreover, we find that adopting arc path instead of square path at the corner locations and “semi-spot vibration” strategy for the offset and fractal deposition patterns respectively can produce better LSFed parts’ quality.

Jun Yu

Papers

First-principles study of the relaxation and energy of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces

Influence of laser deposition patterns on part distortion, interior quality and mechanical properties by laser solid forming (LSF)

Mechanics and energy analysis on molten pool spreading during laser solid forming

Selective Laser Melting (SLM) of in-situ beta phase reinforced Ti/Zr-based bulk metallic glass matrix composite

Performance of different microstructure on electrochemical behaviors of laser solid formed Ti–6Al–4V alloy in NaCl solution