Elevated Temperature Microstructure Stability of SLM 304L Stainless Steel

At elevated temperatures changes in metallurgical structure can be expected for almost any steel or alloy. In stainless steels, the changes can be grain growth, carbide precipitation, ferrite decomposition, or embrittlement. These phenomena can significantly affect the properties of the stainless steel and would potentially change the functionality of the component. Therefore, the impact of elevated temperatures on the microstructure of SLM 304L stainless steel was studied. The work reported here investigates the influence of different aging times at 300C on microstructure and mechanical properties of stainless steels (304L) fabricated with the Selective Laser Melting (SLM) process. Microstructure and mechanical properties were dramatically effected at temperatures much lower than expected when compared to samples of wrought stainless steel. The stainless steel fabricated using the SLM process was more kinetically active than expected based on previous studies of 304L. Results of this study will be presented along with possible reasons for the higher activity.Mechanical Engineerin

A Strategy for Fabrication Complex Structures via a Hybrid Manufacturing Process

The purpose of this paper is to introduce a strategy for fabricating complex structures via a hybrid manufacturing process. The Laser Aided Manufacturing Process (LAMP) lab at Missouri S&T has developed a hybrid process combining both a direct metal deposition process and a five-axis CNC milling. Accessibility is a difficulty when finish machining internal features. The concept is to pause the deposition process to finish machine an internal feature while it is still visible is one possible solution to this issue. However, this must be done in a manner that will not be spoiled when the deposition process continues. This paper discusses processing strategy, tool selection, and experimental validation of a technique to build complex structures via mid-process machining with an undercutting mill.Mechanical Engineerin

An Investigation of the Effect of Direct Metal Deposition Parameters on the Characteristics of the Deposited Layers

Multilayer direct laser deposition (DLD) is a fabrication process through which parts are fabricated by creating a molten pool into which metal powder is injected as particles. During fabrication, complex thermal activity occurs in different regions of the build; for example, newly deposited layers will reheat previously deposited layers. The objective of this study was to provide insight into the thermal activity that occurs during the DLD process. This work focused on the effect of the laser parameters of newly deposited layers on the microstructure and mechanical properties of the previously deposited layers in order to characterize these effects to inform proper parameter selection in future DLD fabrication. Varying the parameters showed to produce different effects on the micro- structure morphology and property values, leading to some tempering and aging of the steels. The microstructure of the top layer was equiaxed, while the near substrate region was fine dendritic. Typically, both the travel speed and laser power significantly affect the microstructure and hardness. Using the commercial ABAQUS/CAE software, a thermo- mechanical 3D finite element model was developed. This work presents a 3D heat transfer model that considers the continuous addition of powder particles in front of a moving laser beam using ABAQUS/CAE software. The model assumes the deposit geometry appropriate to each experimental condition and calculates the temperature distribution, cooling rates and re-melted layer depth, which can affect the final microstructure. Model simulations were qualitatively compared with experimental results acquired in situ using a K-Type thermocouple

Effects of Walking Football During Ramadan Fasting on Heart Rate Variability and Physical Fitness in Healthy Middle-Aged Males

This study aimed to investigate the effect of a walking football (WF) program during Ramadan fasting (RF) on heart rate variability (HRV) indices, body composition, and physical fitness in middle-aged males. Thirty-one healthy sedentary men were randomized to WF ( n = 18) and control ( n = 13) groups. Both groups participated in RF. The WF group were involved in a training program (small-sided games) of three sessions a week during RF. The time and frequency domains of HRV, body composition, handgrip, lumbar strength, Modified Agility Test (MAT), and 6-minute walk test (6MWT) were measured before Ramadan (BR), during Ramadan (DR), and after Ramadan (AR). We reported that RF has significantly altered some parameters of HRV DR; the mean HR decreased while the mean RR, LF, and HF increased. WF had a significant effect on HRV and mean HR DR compared with BR and AR decreased while mean RR, HF and LF increased. DR, body mass decreased in both groups, while body mass index (BMI) decreased and lean mass increased only in WF group. Lower body mass and BMI levels were reported AR only in WF group. Physical capacity improved AR, compared with BR, only in the WF group with longer distance in 6MWT, shorter time(s) in MAT, and higher lumbar strength levels. We conclude that RF increases parasympathetic system activity. WF practice during RF is safe and might improve body composition, physical fitness, autonomic cardiac function, and physical fitness in middle-aged males

Investigation of effect of process parameters on multilayer builds by direct metal deposition

Multilayer direct laser deposition (DLD) is a fabrication process through which parts are fabricated by creating a molten pool into which metal powder is injected as. During fabrication, complex thermal activity occurs in different regions of the build; for example, newly deposited layers will reheat previously deposited layers. The objective of this study was to provide insight into the thermal activity that occurs during the DLD process. This work focused on the effect of the deposition parameters of deposited layers on the microstructure and mechanical properties of the previously deposited layers. Varying the parameters was shown to produce different effects on the microstructure morphology and property values, presumably resulting from in-situ quench and tempering. A commercial ABAQUS/CAE software was used to model this process by developing a thermo-mechanical 3D finite element model. This work presents a 3D heat transfer model that considers the continuous addition of mass in front of a moving laser beam using ABAQUS/CAE software. The model assumes the deposit geometry appropriate to each experimental condition and calculates the temperature distribution, cooling rates and re-melted layer depth, which can affect the final microstructure. Model simulations were qualitatively compared with experimental results acquired in situ using a K-type thermocouple. Moreover, the work focused on the effect of cooling rate and other processing variables on microstructure and mechanical properties. The influence of the cooling rate on the microstructure and mechanical properties was investigated. The differed cooling rate led to varied grain size and resulted in affected varied hardness and tensile strength. --Abstract, page iv

Tensile Test Methodology for PM Components

Component designers often want to know the mechanical properties of press and sinter materials. Usually standard test bars can be used to confirm the properties of a press and sinter alloy, but without actual knowledge of the component properties. This is due to the size of most parts, which does not lend itself to cutting standard samples directly from the component. Subsize tensile samples have been developed and the methodologies for using them worked out. Several PM steels have been evaluated by testing standard test pieces versus subsize samples. Correlation between the two methods will be described and the use of other new methods, such as Automatic Ball Indention will be evaluated. Examples will be given of applications of these subsize specimens to mapping out material properties with location and heat treatment of actual components made from PM steels by press and sintering. With this approach, actual verification of properties can be performed and supplied to purchasers of press and sintered parts

Methodology for Studying Effect of Cooling Rate During Laser Deposition on Microstructure

The present paper focuses on the effect of cooling rate and other processing variables on microstructure and mechanical properties. A specially designed, namely step shape, was used in the current study. The influences of the step thickness were investigated. Results show that the cooling rate is different at different steps and changes the solidification of the deposition process. The cooling rate was deliberately controlled by employing the substrate of varied dimensions. Thermocouples were used to measure the local temperature of the substrate during the deposition process and cooling stage until it reached room temperature. The results of the temperature-time relationship proved the difference in cooling rate. The influence of the substrate dimension on the microstructure and mechanical properties was investigated. The differed cooling rate led to varied grain size and resulted in affected varied hardness and tensile strength. The small samples possessed larger grains sizes formed by a slower cooling rate. The results open the possibility to acquire continuous varied microstructure and mechanical properties by employing a step shape substrate

Component Level Tensile Testing of Press & Sinter Steels

Component designers often want to know the mechanical properties of press and sinter materials. Usually standard test bars can be used to confirm the properties of a press and sinter alloy, but without actual knowledge of the component properties, which can vary significantly. This is due to the size of most parts, which does not lend itself to cutting standard samples directly from the component. Subsize tensile samples have been developed and the methodologies for using them worked out. Examples will be given of applications of these subsize specimens to mapping out material properties with location and heat treatment of actual components made from PM steels by press and sintering. With this approach, actual verification of properties can be performed and supplied to purchasers of press and sintered parts. Property variation with density will also be shown for this methodology

An Investigation of the Effect of Laser Deposition Parameters on Characteristics of Multilayered 316 L Deposits

A potential problem in applying the direct laser deposition (DLD) technique to material fabrication is the effect that subsequent deposited layers have on reheating previous laser deposition layers. Most of the previous investigations examined the effect of the laser deposition parameters on the microstructure and mechanical properties of a single layer. This work focused on the effect of the laser parameters of subsequent layers on the microstructure and mechanical properties of the deposited layers to select proper parameters and characterize the effect. The microstructure morphology and property values are affected by the varied parameters. This leads to some tempering and aging effects in the steels. The microstructure of the top layer was equiaxed, while the near substrate region was fine dendritic. Typically, both of the travel speed and power of the laser show the significant effects on microstructure and hardness

Computational Modelling for Phase Transformation Prediction in Super-Invar Alloys: Analytical and Experimental Data

The possibility of using computational modelling to predict phase transformation processes has been shown while examining super-invar samples. Due to the complicity of phase transformation processes in these alloys the correlation between modelling and experimental work has been described. Modelling allows basic background of composition behavior to be predicted but it doesn`t give the real structure components