Numerical Modeling of Grain Growth in Laser Engineered Net Shaping (LENS) of AISI 316 Stainless Steel

2017 ◽  
Author(s):  
Wenda Tan ◽  
Xuxiao Li
Keyword(s):  
Stainless Steel ◽  
Grain Growth ◽  
Molten Pool ◽  
Grain Structure ◽  
Scale Model ◽  
Modeling Framework ◽  
Laser Engineered Net Shaping ◽  
Macro Scale ◽  
Aisi 316 ◽  
Net Shaping

A multi-scale modeling framework is developed in this work to simulate the transport phenomena and grain growth in Laser Engineered Net Shaping (LENS) process of austenitic stainless steel AISI 316. A three-dimensional (3D) model is included to simulate the transient molten pool geometry and heat/mass transfer on a macro-scale; and a 3D meso-scale model based on the Cellular Automata method is included to predict the grain growth during molten pool solidification. The predicted grain structure is found to be consistent with the experimental results and reveals that the grain structure is highly dependent on the molten pool geometry.

Numerical Modeling of Transport Phenomena and Dendritic Growth in Laser Conduction Welding of 304 Stainless Steel

2011 ◽  
Author(s):  
Wenda Tan ◽  
Neil S. Bailey ◽  
Yung C. Shin
Keyword(s):  
Stainless Steel ◽  
Molten Pool ◽  
Dendritic Growth ◽  
Quantitative Agreement ◽  
304 Stainless Steel ◽  
Experimental Result ◽  
Scale Model ◽  
Transient Model ◽  
Micro Scale ◽  
Macro Scale

A multi-scale model is developed to investigate the heat/mass transport and dendrite growth in laser spot conduction welding. A macro-scale transient model of heat transport and fluid flow is built to study the evolution of temperature and velocity field of the molten pool. The molten pool geometry and other solidification parameters are calculated, and the predicted pool geometry matches well with experimental result. On the micro-scale level, the dendritic growth of 304 stainless steel is simulated by a novel model that has coupled the Cellular Automata (CA) and Phase Field (PF) methods. The epitaxial growth is accurately identified by defining both the grain density and dendrite arm density at the fusion line. By applying the macro-scale thermal history onto the micro-scale calculation domain, the microstructure evolution of the entire molten pool is simulated. The predicted microstructure achieves a good quantitative agreement with the experimental results.

scholarly journals Imaging Hydrogen in Stainless Steel Alloys by Kelvin Probe Force Microscopy

2018 ◽  
Author(s):  
J. D. McNamara ◽  
A. J. Duncan ◽  
M. J. Morgan ◽  
P. S. Korinko
Keyword(s):  
Stainless Steel ◽  
Grain Boundaries ◽  
Contact Potential Difference ◽  
Kelvin Probe Force Microscopy ◽  
Grain Structure ◽  
Kelvin Probe ◽  
Contact Potential ◽  
Steel Alloys ◽  
Force Microscopy ◽  
Net Shaping

Kelvin probe force microscopy (KPFM) was used to image austenitic stainless steel (SS) samples (Type 304L) fabricated by the laser engineered net shaping (LENS®) process. The samples were hydrogen charged (H-charged) and subsequently cut and polished. The surface contact potential difference (CPD) of the samples was measured using the KPFM technique, a form of atomic force microscopy. A set of uncharged samples was also studied for reference and changes in the CPD were on the noise level. For H-charged samples fabricated by the LENS® process, the resulting surface potential images show a change in CPD of about 10 – 20mV around cell-like boundaries (5–10 μm in size) and grain boundaries (50–100 μm in size). The significant change in the CPD is affected by variation of the local work function, which indicates the presence of hydrogen. The elemental composition of the LENS® samples was studied using energy dispersive spectroscopy (EDS) which showed an increase in the atomic percentage of Cr and a decrease in Ni around the cell-like boundaries. The existence of intercellular ferrite on the sub-grain boundaries may explain the propensity of hydrogen to segregate around these regions. The finer grain structure of LENS® samples compared to that of forged or welded samples suggests that the hydrogen can be dispersed differently throughout this material than in traditionally forged austenitic SS. This study is conducted to elucidate the behavior of hydrogen with respect to the microstructure of additively manufactured stainless steel alloys.

scholarly journals Comparative Quality Control of Titanium Alloy Ti–6Al–4V, 17–4 PH Stainless Steel, and Aluminum Alloy 4047 Either Manufactured or Repaired by Laser Engineered Net Shaping (LENS)

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4171 ◽  
Author(s):  
Noam Eliaz ◽  
Nitzan Foucks ◽  
Dolev Geva ◽  
Shai Oren ◽  
Noy Shriki ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
High Standard ◽  
Micro Computed Tomography ◽  
Laser Engineered Net Shaping ◽  
Ct Analysis ◽  
Powder Particles ◽  
Structural Parts ◽  
Net Shaping ◽  
Roughness Measurements

Additive manufacturing attracts much interest for manufacturing and repair of structural parts for the aerospace industry. This paper presents comparative characterization of aircraft items made of Al 4047 alloy, Ti-6Al-4V alloy, and 17-4 precipitation hardened (PH) (AISI 630) stainless steel, either manufactured or repaired by laser engineered net shaping (LENS). Chemical analysis, density, and surface roughness measurements, X-ray micro-computed tomography (μ-CT) analysis, metallography, and micro-hardness testing were conducted. In all three materials, microstructures typical of rapid solidification were observed, along with high density, chemical composition, and hardness comparable to those of the counterpart wrought alloys (even in hard condition). High standard deviation in hardness values, anisotropic geometrical distortion, and overbuild at top edges were observed. The detected defects included partially melted and unmelted powder particles, porosity, and interlayer lack of fusion, in particular at the interface between the substrate plate and the build. There was a fairly good match between the density values measured by μ-CT and those measured by the Archimedes method; there was also good correlation between the type of defects detected by both techniques. Surface roughness, density of partially melted powder particles, and the content of bulk defects were significantly higher in Al 4047 than in 17-4 PH stainless steel and Ti-6Al-4V alloy. Optical gaging can be used reliably for surface roughness measurements. The implications of these findings are discussed.

Study of the Metallurgy of a Dissimilar Ti-6Al-4V – Stainless Steel Linear Fiction Welded Joints

2015 ◽  
Vol 651-653 ◽  
pp. 1427-1432 ◽  
Author(s):  
Filomena Impero ◽  
Fabio Scherillo ◽  
Antonello Astarita ◽  
Kathryn A. Beamish ◽  
Michele Curioni ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Intermetallic Compounds ◽  
Weld Line ◽  
Beta Phase ◽  
Alpha Phase ◽  
Parent Material ◽  
Grain Structure ◽  
Linear Friction ◽  
Aisi 316 ◽  
Welding Processes

This paper deals with the investigation of the metallurgy of a dissimilar Ti-6Al-4V-stainless steel joint linear friction welded. In particular two different stainless steel were considered: AISI 304 and AISI 316. These two alloys differs in the Molybdemun content. Metallographic observations, EDS analysis and Vickers Microhardness measurements were carried out, particular attention was focused on the study of the intermetallic compounds and on the microstructures of the different zones produced by the process. As usual for solid state welding processes, three different zones can be identified: the parent material, the heat affected zone (HAZ) and the thermo-mechanical affected zone (TMAZ), furthermore a very thin joining line, rich of intermetallic compounds, was also observed. In this zone diffusive phenomena also occurred resulting in a variation of the alpha phase content on the titanium side.In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Moreover it was observed that in the weld region, exposure to supertransus temperatures (995°C) combined with hot-deformation working and rapid cooling after joining induced the recrystallization of a martensitic beta grain structure. Concerning the joint between Ti-6Al-4V and AISI 316 some cracks were observed within the weld line, this due to the presence of brittle intermetallics compounds in this zone. The formation of these intermetallics was promoted by the presence of Molybdenum.

A Study on Laser Engineered Net Shaping Prototyping Technology

2007 ◽  
Author(s):  
Z. Xu ◽  
R. S. Amano ◽  
J. M. Lucci ◽  
Steven Gerard Marek ◽  
Pradeep Rohatgi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Stainless Steel ◽  
Numerical Method ◽  
Cooling Rate ◽  
Process Parameters ◽  
316L Stainless Steel ◽  
Point Of View ◽  
Simplified Models ◽  
Laser Engineered Net Shaping ◽  
Net Shaping

The objectives of this work are to study Laser Engineered Net Shaping (LENS™) produced materials and identify the microstructures. Numerical method was used to examine the influence of materials’ type and LENS™ process parameters on the forming of the specific microstructures from thermodynamics and fluid dynamics point of view. Samples of 316L stainless steel were examined, microstructures of samples were used to estimate the corresponding cooling rate, and the cooling rate was compared with the results of three different level of simplified models.

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