A Review of Heat Treatments on Improving the Quality and Residual Stresses of the Ti–6Al–4V Parts Produced by Additive Manufacturing

Comparison of the Microstructural, Mechanical and Corrosion Resistance Properties of Ti6Al4V Samples Manufactured by LENS and Subjected to Various Heat Treatments

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C.

An Overview of the Latest Progress in Internal Surface Finishing of the Additively Manufactured Metallic Components

Fast progress in near-net-shape production of parts has attracted vast interest in internal surface finishing. Interest in designing a modern finishing machine to cover the different shapes of workpieces with different materials has risen recently, and the current state of technology cannot satisfy the high requirements for finishing internal channels in metal-additive-manufactured parts. Therefore, in this work, an effort has been made to close the current gaps. This literature review aims to trace the development of different non-traditional internal surface finishing methods. For this reason, attention is focused on the working principles, capabilities, and limitations of the most applicable processes, such as internal magnetic abrasive finishing, abrasive flow machining, fluidized bed machining, cavitation abrasive finishing, and electrochemical machining. Thereafter, a comparison is presented based on which models were surveyed in detail, with particular attention to their specifications and methods. The assessment is measured by seven key features, with two selected methods deciding their value for a proper hybrid machine.

Study on the Process Characteristics Based on Joule Heat of Sliding-Pressure Additive Manufacturing

This study developed an experimental system based on Joule heat of sliding-pressure additive manufacturing (SP-JHAM), and Joule heat was used for the first time to accomplish high-quality single-layer printing. The roller wire substrate is short-circuited, and Joule heat is generated to melt the wire when the current passes through. Through the self-lapping experimental platform, single-factor experiments were designed to study the effects of power supply current, electrode pressure, contact length on the surface morphology and cross-section geometric characteristics of the single-pass printing layer. Through the Taguchi method, the effect of various factors was analyzed, the optimal process parameters were obtained, and the quality was detected. The results show that with the current increase, the aspect ratio and dilution rate of a printing layer increase within a given range of process parameters. In addition, with the increase in pressure and contact length, the aspect ratio and dilution ratio decrease. Pressure has the greatest effect on the aspect ratio and dilution ratio, followed by current and contact length. When a current of 260 A, a pressure of 0.60 N and a contact length of 1.3 mm are applied, a single track with a good appearance, whose surface roughness Ra is 3.896 μm, can be printed. Additionally, the wire and the substrate are completely metallurgically bonded with this condition. There are also no defects such as air holes and cracks. This study verified the feasibility of SP-JHAM as a new additive manufacturing strategy with high quality and low cost, and provided a reference for developing additive manufacturing technology based on Joule heat.

Direct Metal Laser Sintering of the Ti6Al4V Alloy from a Powder Blend

Additively manufactured Ti6Al4V parts have only seen major application in industries such as the aerospace and medical industries, mainly due to the high cost of production of the feedstock powder. In this article, the feasibility of in situ alloying a powder blend of elemental Ti and an Al-V master alloy to produce the Ti6Al4V alloy through direct metal laser sintering is presented and discussed. In a previous study, single track formation from this powder blend was studied and analyzed to determine the optimum principal process parameters suitable for this powder blend. These process parameters were employed in this study to produce single and double layers where the effects of varied hatch distance and the employment of a rescanning strategy on the surface morphology and alloy homogeneity were investigated. Lastly, in the current study, three-dimensional specimens were produced and analyzed to determine the alloy microstructure, homogeneity, part porosity and mechanical properties. The analyses revealed that a Ti6Al4V alloy with a density of up to 99.9% and corresponding tensile strength and ductility values of up to 942.9 MPa and 17% was produced. Furthermore, a minimum Al evaporation value of 7.2% was recorded. Therefore, in situ alloying can indeed be employed to produce high-quality Ti6Al4V parts from an elemental Ti and an Al-V master alloy powder blend.

Additive Manufacturing of AlSi10Mg and Ti6Al4V Lightweight Alloys via Laser Powder Bed Fusion: A Review of Heat Treatments Effects

Laser powder bed fusion (L-PBF) is an additive manufacturing technology that is gaining increasing interest in aerospace, automotive and biomedical applications due to the possibility of processing lightweight alloys such as AlSi10Mg and Ti6Al4V. Both these alloys have microstructures and mechanical properties that are strictly related to the type of heat treatment applied after the L-PBF process. The present review aimed to summarize the state of the art in terms of the microstructural morphology and consequent mechanical performance of these materials after different heat treatments. While optimization of the post-process heat treatment is key to obtaining excellent mechanical properties, the first requirement is to manufacture high quality and fully dense samples. Therefore, effects induced by the L-PBF process parameters and build platform temperatures were also summarized. In addition, effects induced by stress relief, annealing, solution, artificial and direct aging, hot isostatic pressing, and mixed heat treatments were reviewed for AlSi10Mg and Ti6AlV samples, highlighting variations in microstructure and corrosion resistance and consequent fracture mechanisms.

Machine Learning Based Predictions of Fatigue Crack Growth Rate of Additively Manufactured Ti6Al4V

The present work focusses on machine learning assisted predictions of the fatigue crack growth rate (FCGR) of Ti6Al4V (Ti64) processed through laser powder bed fusion (L-PBF) and post processing. Various machine learning techniques have provided a flexible approach for explaining the complex mathematical interrelationship among processing-structure-property of the materials. In the present work, four machine learning (ML) algorithms, such as K- Nearest Neighbor (KNN), Decision Trees (DT), Random Forests (RF), and Extreme Gradient Boosting (XGB) algorithms are implemented to analyze the Fatigue Crack growth rate (FCGR) of Ti64 alloy. After tuning the hyper parameters for these algorithms, the trained models were found to estimate the unseen data as equally well as the trained data. The four tested ML models are compared with each other over the training as well as testing phase, based on their mean squared error and R2 scores. Extreme Gradient Boosting has performed better for the FCGR predictions providing least mean squared errors and higher R2 scores compared to other models.

Friction Stir Processing of Additively Manufactured Ti-6Al-4V Alloy: Structure Modification and Mechanical Properties

This work explores the possibility of using friction stir processing to harden the Ti-6Al-4V titanium alloy material produced by wire-feed electron beam additive manufacturing. For this purpose, thin-walled workpieces of titanium alloy with a height of 30 cm were printed and, after preparation, processed with an FSW-tool made of heat-resistant nickel-based superalloy ZhS6U according to four modes. Studies have shown that the material structure and properties are sensitive to changes in the tool loading force. In contrast, the additive material’s processing direction, relative to the columnar grain growth direction, has no effect. It is shown that increasing the axial load leads to forming a 𝛽-transformed structure and deteriorates the material strength. At the same time, compared to the additive material, the ultimate tensile strength increase during friction stir processing can achieve 34–69%.

Influence of Postprocessing on Wear Resistance of Aerospace Steel Parts Produced by Laser Powder Bed Fusion

The paper is devoted to the research of the effect of ultrasonic postprocessing—specifically, the effects of ultrasonic cavitation-abrasive finishing, ultrasonic plastic deformation, and vibration tumbling on surface quality, wear resistance, and the ability of real aircraft parts with complex geometries and with sizes less than and more than 100 mm to work in exploitation conditions. The parts were produced by laser powder bed fusion from two types of anticorrosion steels of austenitic and martensitic grades—20Kh13 (DIN 1.4021, X20Cr13, AISI 420) and 12Kh18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321). The finishing technologies based on mechanical action—plastic deformation, abrasive wear, and complex mechanolysis showed an effect on reducing the submicron surface roughness, removing the trapped powder granules from the manufactured functional surfaces and their wear resistance. The tests were completed by proving resistance of the produced parts to exploitation conditions—vibration fatigue and corrosion in salt fog. The roughness arithmetic mean deviation Ra was improved by 50–52% after cavitation-abrasive finishing, by 28–30% after ultrasonic plastic deformation, and by 65–70% after vibratory tumbling. The effect on wear resistance is correlated with the improved roughness. The effect of used techniques on resistance to abrasive wear was explained and grounded.

Effect of Cavitation Erosion Wear, Vibration Tumbling, and Heat Treatment on Additively Manufactured Surface Quality and Properties

The paper is devoted to researching various post-processing methods that affect surface quality, physical properties, and mechanical properties of laser additively manufactured steel parts. The samples made of two types of anticorrosion steels—20kH13 (DIN 1.4021, X20Cr13, AISI 420) and 12kH18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321) steels—of martensitic and austenitic class were subjected to cavitation abrasive finishing and vibration tumbling. The roughness parameter Ra was reduced by 4.2 times for the 20kH13 (X20Cr13) sample by cavitation-abrasive finishing when the roughness parameter Ra for 12kH18N9T (X10CrNiTi18-10) sample was reduced by 2.8 times by vibratory tumbling. The factors of cavitation-abrasive finishing were quantitatively evaluated and mathematically supported. The samples after low tempering at 240 °C in air, at 680 °C in oil, and annealing at 760 °C in air were compared with cast samples after quenching at 1030 °C and tempering at 240 °C in air, 680 °C in oil. It was shown that the strength characteristics increased by ~15% for 20kH13 (X20Cr13) steel and ~20% for 12kH18N9T (X10CrNiTi18-10) steel than for traditionally heat-treated cast samples. The wear resistance of 20kH13 (X20Cr13) steel during abrasive wear correlated with measured hardness and decreased with an increase in tempering temperatures.