A Novel Approach for Real-Time Quality Monitoring in Machining of Aerospace Alloy through Acoustic Emission Signal Transformation for DNN

Gamma titanium aluminide (γ-TiAl) is considered a high-performance, low-density replacement for nickel-based superalloys in the aerospace industry due to its high specific strength, which is retained at temperatures above 800 °C. However, low damage tolerance, i.e., brittle material behavior with a propensity to rapid crack propagation, has limited the application of γ-TiAl. Any cracks introduced during manufacturing would dramatically lower the useful (fatigue) life of γ-TiAl components, making the workpiece surface’s quality from finish machining a critical component to product quality and performance. To address this issue and enable more widespread use of γ-TiAl, this research aims to develop a real-time non-destructive evaluation (NDE) quality monitoring technique based on acoustic emission (AE) signals, wavelet transform, and deep neural networks (DNN). Previous efforts have opted for traditional approaches to AE signal analysis, using statistical feature extraction and classification, which face challenges such as the extraction of good/relevant features and low classification accuracy. Hence, this work proposes a novel AI-enabled method that uses a convolutional neural network (CNN) to extract rich and relevant features from a two-dimensional image representation of 1D time-domain AE signals (known as scalograms), subsequently classifying the AE signature based on pedigreed experimental data and finally predicting the process-induced surface quality. The results of the present work show good classification accuracy of 80.83% using scalogram images, in-situ experimental data, and a VGG-19 pre-trained neural network, establishing the significant potential for real-time quality monitoring in manufacturing processes

IN-SITU CHARACTERIZATION OF SURFACE QUALITY IN γ-TiAl AEROSPACE ALLOY MACHINING

The functional performance of critical aerospace components such as low-pressure turbine blades is highly dependent on both the material property and machining induced surface integrity. Many resources have been invested in developing novel metallic, ceramic, and composite materials, such as gamma-titanium aluminide (γ-TiAl), capable of improved product and process performance. However, while γ-TiAl is known for its excellent performance in high-temperature operating environments, it lacks the manufacturing science necessary to process them efficiently under manufacturing-specific thermomechanical regimes. Current finish machining efforts have resulted in poor surface integrity of the machined component with defects such as surface cracks, deformed lamellae, and strain hardening. This study adopted a novel in-situ high-speed characterization testbed to investigate the finish machining of titanium aluminide alloys under a dry cutting condition to address these challenges. The research findings provided insight into material response, good cutting parameter boundaries, process physics, crack initiation, and crack propagation mechanism. The workpiece sub-surface deformations were observed using a high-speed camera and optical microscope setup, providing insights into chip formation and surface morphology. Post-mortem analysis of the surface cracking modes and fracture depths estimation were recorded with the use of an upright microscope and scanning white light interferometry, In addition, a non-destructive evaluation (NDE) quality monitoring technique based on acoustic emission (AE) signals, wavelet transform, and deep neural networks (DNN) was developed to achieve a real-time total volume crack monitoring capability. This approach showed good classification accuracy of 80.83% using scalogram images, in-situ experimental data, and a VGG-19 pre-trained neural network, thereby establishing the significant potential for real-time quality monitoring in manufacturing processes. The findings from this present study set the tone for creating a digital process twin (DPT) framework capable of obtaining more aggressive yet reliable manufacturing parameters and monitoring techniques for processing turbine alloys and improving industry manufacturing performance and energy efficiency

Launch vehicle flight control augmentation using smart materials and advanced composites (CDDF Project 93-05)

The Marshall Space Flight Center has a rich heritage of launch vehicles that have used aerodynamic surfaces for flight stability such as the Saturn vehicles and flight control such as on the Redstone. Recently, due to aft center-of-gravity locations on launch vehicles currently being studied, the need has arisen for the vehicle control augmentation that is provided by these flight controls. Aerodynamic flight control can also reduce engine gimbaling requirements, provide actuator failure protection, enhance crew safety, and increase vehicle reliability, and payload capability. In the Saturn era, NASA went to the Moon with 300 sq ft of aerodynamic surfaces on the Saturn V. Since those days, the wealth of smart materials and advanced composites that have been developed allow for the design of very lightweight, strong, and innovative launch vehicle flight control surfaces. This paper presents an overview of the advanced composites and smart materials that are directly applicable to launch vehicle control surfaces

Abrasive Waterjet Turning of High Performance Materials

AbstractThe cutting of high performance materials requires specific machine tools and cutting tools. The wear resistance of cutting tools is important for turning of hypereutectic aluminium silicon or titanium aluminide alloys. Abrasive waterjet turning has been shown to be a suitable cutting process for these challenging materials. The tool life time of at least 10hours combined with a material removal rate of up to 0.8cm3/min and low process temperatures give this cutting technology a very high potential. Furthermore the material close to the cutting surface is less modified compared to conventional rough turning. The same effects are of particular interest with regard to the functional capability of waterjet turned γ-TiAl-alloys

Synthesis, microstructure and mechanical properties of bulk ultrafine grained Ti-47Al-2Cr (at%) alloy

Hot isostatic pressing (HIP) and powder compact forging of Ti/Al/Cr composite powders of composition Ti-47Al-2Cr (at%) have been carried out to synthesize bulk ultrafine grained Ti-47Al-2Cr alloy. The Ti/Al/Cr composite powders were produced using high energy mechanical milling of elemental Ti, Al, Cr powders in a retsch planetary mill. The microstructure and mechanical properties of the bulk consolidated alloy produced using different processing techniques has been investigated. The mechanical properties of the alloy were studied in tension and compression both at room and elevated temperatures especially to know the formability of the material. The bulk alloy samples produced by HIP for 2 hours at 1000 degrees C had porosity of approximately ~ 5%, indicating that the HIP time was not sufficient to close the pores. The microstructure mainly consisted of TiAl as the major phase and Ti(Al) and Ti3Al as minors, the unreacted Ti(Al) phase in the microstructure was mainly due to the initial powder condition, in which a small fraction of powder particles were rich in Ti. Tensile testing of the alloy samples was carried out at different temperatures. At room temperature the alloy was fairly brittle, without any plastic deformation, and had a fracture strength of ~ 100 MPa. At elevated temperatures the samples became ductile, as reflected by considerable amounts of tensile elongations at 800 degrees C and above. The maximum amount of elongation was found to be between 70 - 80% at 900 degrees C. The tensile yield strength at 800 degrees C was in the range of 84-90 MPa and decreased to 55-58 MPa with the testing temperature of the samples to 900 degrees C. In compression the alloy showed plastic yielding and yield strength of ~ 1.4 GPa at room temperature. Compression testing at 900 degrees C revealed that compressive deformations equivalent to a height reduction of 50% could be easily achieved without cracking. Direct powder compact forging using canned powder compacts of the Ti/Al/Cr composite powder was successfully used to produce bulk consolidated Ti-47Al-2Cr alloy samples. It has been observed that the density of the bulk consolidated alloy sample after forging varied from the centre to the periphery. XRD analysis showed that the forged samples, consisted of TiAl (as major phase) along with Ti(Al) and Ti3.3Al phases. Mechanical testing of the samples showed that the samples exhibited brittle type of fracture both in tension and compression at room temperature and the fracture strength of the samples was in the range of 115 - 130 MPa in tension and 1.38-1.4 GPa in compression without any yielding. When being tested at 900 degrees C, the samples became very ductile showing yield strength in the range of 70-90 MPa and elongation to fracture between 80-165% in tension, and a yield strength of ~ 65 MPa and 50% deformation in compression was easily achievable. Nearly fully dense Ti-47-2Cr alloy samples with density of ~98% were produced by using HIP at 1000 degrees C for a duration of 3 hours. TEM observations revealed equiaxed grains with grain sizes in the range of 200-500 nm. The tensile testing of the alloy samples at different temperatures revealed that the brittle to ductile transition temperature of the alloy was in the range of 700 and 750 degrees C, similar to that reported from literatures. The alloy showed significantly higher strengths both at room and at elevated temperatures, due to the low level of porosity in the sample. Elongation of 95 - 117% at 750 degrees C and 70-100% at 800 degrees C was observed. The ultrafine grained Ti-47Al-2Cr alloy produced using a combination of mechanical milling and HIP/powder compact forging has demonstrated good formability at elevated temperatures leaving a large space for secondary processing to improve the quality of the material

Kinetics of high-temperature oxidation of (Ti,Ta)(CN)-based cermets

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.Gobierno de España European Regional Development MAT2011- 2298

Kinetics of high-temperature oxidation of (Ti,Ta)(CN)-based cermets

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.Peer reviewe

Advanced Powder Metallurgy Technologies

Powder metallurgy is a group of advanced processes used for the synthesis, processing, and shaping of various kinds of materials. Initially inspired by ceramics processing, the methodology comprising the production of a powder and its transformation to a compact solid product has attracted attention since the end of World War II. At present, many technologies are availabe for powder production (e.g., gas atomization of the melt, chemical reduction, milling, and mechanical alloying) and its consolidation (e.g., pressing and sintering, hot isostatic pressing, and spark plasma sintering). The most promising methods can achieve an ultra-fine or nano-grained powder structure, and preserve it during consolidation. Among these methods, mechanical alloying and spark plasma sintering play a key role. This book places special focus on advances in mechanical alloying, spark plasma sintering, and self-propagating high-temperature synthesis methods, as well as on the role of these processes in the development of new materials

Review of current best-practices in machinability evaluation and understanding for improving machining performance

Machinability is a generalized framework that attempts to quantify the response of a workpiece material to mechanical cutting, which has been developed as one of the key factors that drive the final selection of cutting parameters, tools, and coolant applications. Over the years, there are many attempts have been made to develop a standard evaluation method of machinability. However, due to the complexity of the influence factors, i.e., from work material and cutting tool to machine tool, that can affect the materials machinability, currently there is no uniquely defined quantification of machinability. As one of the outcomes from the CIRP's Collaborative Working Group on “Integrated Machining Performance for Assessment of Cutting Tools (IMPACT)”, this paper conducts an extensive study to learn interacting machinability parameters to evaluate the overall machining performance. Specifically, attention is focused on recent advances made towards the determination of the machinability through tool wear, cutting force and temperature, chip form and breakability, as well as the surface integrity. Furthermore, the advanced methods that have been developed over the years to enable the improvement of machinability have been reviewed