Duplex Aging and Gas Nitriding Process as a Method of Surface Modification of Titanium Alloys for Aircraft Applications

This study discusses the effect of a duplex aging + nitriding process on the wear resistance of an aged double-phase titanium alloy, BT22. Nitriding was applied simultaneously with the heat treatment of the alloy, which is advantageous over the conventional heat and surface treatment methods applied to titanium alloys. According to the results, the thickness of the case depth of the nitrided samples was 40–50 μm. Moreover, nitrogen was uniformly dispersed in the substrate, which was indicated by the hardness tests. The average microhardness of the substrate material was 300 HV0.01, while the hardness of the top layer was 1190 HV0.01, which is an almost four-fold increase. The applied duplex treatment substantially affected the wear performance of the tested alloy. For the untreated alloy, the maximum coefficient of friction was 0.8, while in the surface-modified sample, the maximum fluctuations reached 0.6. The abrasive wear process was dominant in the nitrided samples, while delamination and adhesive wear were observed for the untreated specimens. The nitrided alloy exhibited double the wear resistance of the untreated samples. The proposed treatment does not require additional time or energy consumption, providing a substantial technological advantage over conventional methods. Though the alpha case reduces the mechanical performance of titanium, the nitriding of only the component sections intended to withstand friction will have a positive effect.

Does 3D-Printed Coil Perform Better for Induction Hardening and How to Predict the Performance Based on Numerical Simulation?

Recent developments in additive manufacturing (also called 3D printing of inductors) have opened new possibilities in the induction heating field by making inductors that have a longer service life and are more reproducible. Computer simulations were done to compare inductors made with two different techniques – conventional manufacturing and additive manufacturing. To compare inductor performance, heating of the soldered joints, the change in power consumption in the inductors and the temperature field in the workpiece were studied. Also, different steel structures such as austenite, bainite, pearlite, and martensite were studied to measure the case depth of the workpiece. All calculations were done by using CENOS simulation software, which uses a coupled electromagnetic-thermal model to describe the induction heating process. For the phase transition calculations a time temperature transformation diagram was used.

Relationship Between Deep Case Carburizing and Residual Stress in Rolling Contact Service

The proposition that compressive residual stresses are beneficial in improving the service life of components subject to rolling contact fatigue is well documented. However, the exact nature of the relationship between effective case depth (ECD) and the residual stress state is not well understood for components with deep case depth (>0.050inches, 1.27mm). It is expected that compressive residual stresses will gradually transition to tensile stresses as the case depth increases beyond a threshold value. In addition, the strain-induced transformation of retained austenite and its influence on the residual stress state of components resulting from service will be explored. This study will measure the residual stress state of components prepared with various ECD before and after simulated service with the goal of determining where the compressive to tensile transition occurs. Residual stress and retained austenite measurements will be conducted using X-ray diffraction.

Investigating the Benefits of Using 3D Camera Technology to Improve Wound Measurements in a Tissue Viability Service: Outcomes of a Pilot Implementation Study

Sub-optimal experience and outcomes for people with stalled wounds is common. Clinicians have limited methods for reliably and accurately measure wounds. Depth measurement is an important indicator of healing, and digital methods of imaging the wound may offer increased accuracy and enable clinical decision-making. This study aimed to implement a Panasonic FZ-M1 toughpad with WoundCareLite software version 1.5.0.0, to enable three-dimensional measurements in Tissue Viability (TV) service. Length, width, and depth measurement were compared with usual manual measurement using a paper ruler alongside a 2D photographic image. Statistical analysis included the comparison of wound dimension measures and a presentation of visual healing trajectories over 4 weeks using run-charts. 30 patients were recruited over five weeks (13 female and 17 male), representing 4% of the usual caseload. Manual measurement and 3D software automatic method demonstrated that the width and depth 3D auto measures were more accurate than manual measures but depth measures were often wrong thus making volumetric measures inaccurate. Consistent wound size measurement was feasible, and healing trajectories provide a useful means of continuous assessment. Technology guided measurement has potential benefits over manual measurement as a means of more accurately monitoring healing. In this case, depth measurement could not be accurately assessed in practice and further software innovation is indicated to enable outcome measurement in tissue viability services.

Influence of carbonitriding conditions on phase composition and residual stresses for 20MnCr5 low alloy steel

This paper reports an investigation of the influence of carbonitriding conditions for 20MnCr5 low alloy steel. Three gaseous carbonitriding conditions were investigated based on different carbon and nitrogen potentials to attain varying levels of carbon between 0.62 and 0.93% mass, whereas for nitrogen between 0.19 and 0.26% mass at the surface. Analysis of retained austenite and residual stress distributions was conducted using X-ray diffraction technique. The effective case depth varied between 900 and 1200 µm. The case microstructures were characterized by varying proportions of retained austenite and martensite, while the core contained essentially bainitic microstructures. The maximum amount of retained austenite which occurred at a depth of 50 µm from the subsurface ranged between 30 and 70% mass and significantly influenced the level of surface micro-hardness whereas the core hardness remaining relatively constant at 450 HV1. High values of residual stresses in martensite phase were observed. The signs, magnitudes, distributions and location of maximum compressive residual stresses were highly influenced by the maximum fraction of retained austenite. Retained austenite of 30%, 50% and 70% mass at the surface lead to peak compressive residue stresses of -280, -227, and -202 MPa at depths of 555, 704, and 890 μm, respectively. Keywords: Carbonitriding, retained austenite, martensite, residual stress, XRD.

The Relationship between Surface and In-Depth Hardness for the Nitrocarburizing Treatment Process

The aim of this study is to exhibit the mutual connection between surface and in depth hardness values in the case of surface-treated metal samples with inhomogeneous hardness distribution in the surface layer. The reason for surface treatments of metal alloys is most commonly to increase the hardness and wear resistance at the surface. Case depth, as a result of surface treatment and the in-depth hardness distribution, can be determined by measuring the hardness of a section perpendicular to the treated surface and by metallographic examination. The result of heat treatment can also be checked rapidly by surface hardness testing. Surface hardness carries only indirect information regarding case depth and hardness distribution. Surface and cross-sectional hardness can be related to the mathematical modeling of the plastic zone developing in the indentation process. The mathematical model applied in this study allows the conversion of the surface hardness function into the in-depth hardness function and vice-versa. The calculation method presented was validated by analyzing the hardness data of nitrocarburized samples of various case depths. The validation result proves that cross-sectional hardness distribution can be adequately estimated by surface hardness data in the case of a surface layer with monotonically decreasing hardness distribution.

A Novel Investigation Into the Edge Effect Reduction of 4340 Steel Disc Through Induction Hardening Process Using Magnetic Flux Concentrators

Induction hardening serves as one of the best mass production processes used recently due to its ability to quickly generating high-intensity heat in a well-defined location of the part. Numerous advantages of this method make it a reliable technique to produce a thin martensite layer on the part surface that has compressive residual stresses. In this regard, the presented study is devoted to investigating utilizing induction heating for surface hardening of AISI 4340 steel disc. The purpose is to evaluate the performance of magnetic flux concentrators and the effects of the induction process parameter on the case-depth and edge effect in the surface hardening of the disc. Once the proper range of parameters is defined, Taguchi experimentation planning is used to frame comprehensive experimentation with the minimum possible trial. Then, the case-depth of discs is evaluated on their cross-sections (edge and middle plane) through hardness profile measurement of samples using a micro-indentation hardness machine. The results are then statistically analyzed using Analysis of Variance (ANOVA) and Response Surface Methodology (RSM) to determine the best combination of parameters to achieve maximum case-depth yet minimum edge effect. The goodness-of-fit regression models are then developed to predict the case-depth profile as a function of machine parameters based on linear regression utilizing case-depth responses in the edge and middle plane of discs. Results imply that maximum case-depth with minimum edge effect can be produced by using the highest heating time along with the average amplitude of the power, axial gap, and radial gap. This study gives a good exploration of case-depths optimized by setting up process parameters when magnetic flux concentrator is utilized, thus, a guideline to reduce discs edge effect in induction surface hardening application is given.

The Effect of Chip Binding on the Parameters of the Case-Hardened Layer of Tooth Surfaces for AMS 6308 Steel Gears Processed by Thermochemical Treatment

The following article describes influence of pressure welded or bound chips to the gear tooth flank and/or the tooth root on a carburized case and surface layer hardness of Pyrowear 53 steel gears, machined by Power Skiving method. This paper is focused only on one factor, the chips generated while forming gear teeth by power skiving, which could result in local changes in the carburized case parameters as a negatively affecting point of mechanical performance of the carburized case. The chips, due to the specifics of the power skiving process and the kinematics of tooth forming, could be subject to the phenomena of pressure welding or binding of chips to the tooth. During the carburizing stage of the downstream manufacturing processes, the chips form a diffusion barrier, which ultimately could result in localized changes in the carburized case. This work was an attempt to answer the question of how and to what extent the chips affect the case hardening. Performed simulations of chips by a generating cupper “spots”, mentioned in the study, represent a new approach in connection with minimization of errors, which could appear during carbon case depth and case hardness analysis for typical chips, generated during the machining process—assurance that a complete chip was bound to the surface. Hardness correlation for zones, where the chip appears with areas free of chips, gives simple techniques for assessment. Performed tests increased the knowledge about the critical size of the chip—1.5 mm, which could affect the case hardening. Obtained experimental test results showed that the appearance of chip phenomena on the gear tooth might have a negative impact on a carburized case depth and hardened layer.

Microstructure, Hardness, and Tensile Properties of Vacuum Carburizing Gear Steel

We investigated the effects of the austenitizing temperature on the microstructure, hardness, and tensile properties of case-carburized steel after vacuum carburization at 930 °C and then re-austenitization at 820–900 °C followed by oil quenching and tempering. The results show that fractures occurred early with the increase in the austenitizing temperature, although all the carburized specimens showed a similar case hardness of 800 HV0.2 and case depth of 1.2 mm. The highest fracture stress of 1919 MPa was obtained for the experimental steel when the austenitizing temperature was 840 °C due to its fine microstructure and relatively high percentage of retained austenite transformed into martensite during the tensile tests. We also found that the stress–strain behavior of case-carburized specimens could be described by the area-weighted curves of the carburized case and the core in combination. The strain hardening exponent was about 0.4 and did not vary with the increase in the austenitizing temperature. We concluded that the optimum austenitizing temperature was around 840 °C for the experimental steel.