Hot deformation behavior of 60NiTi shape-memory alloy fabricated by hot isostatic pressing

The 60NiTi (Ni60wt%–Ti40wt%) intermetallic is a hard-to-process material. Understanding of hot deformation behavior is crucial for the hot working of 60NiTi. This work studied hot deformation behavior and corresponding microstructure of the hot isostatic pressed 60NiTi in the temperature range of 900 °C–1050 °C and at strain rates of 0.1, 0.01, and 0.001 s-1 through a hot compression test. The flow stress and microstructure were susceptible to the hot deformation parameters. The flow stress decreased with the increase in deformation temperature and decrease in strain rate. Work hardening occurred at a small strain, then followed by softening; finally, near-dynamic equilibrium was achieved between work hardening and softening. A constitutive equation was developed to describe the effects of strain rate and temperature on flow stress. Simulation of hot deformation via the finite element method revealed the workpiece’s inhomogeneous deformation. The deformation occurred mainly in the center area of the cylindrical sample, resulting in high stress and strain concentrations in this region and causing the equiaxial grains to be compressed into prolate grains. This work can provide guidance for the hot working, such as forging and hot rolling, of 60NiTi.

Hybrid additive manufacturing of hot working tool steel H13 with dissimilar base bodies using Laser-based Powder Bed Fusion

Hybrid additive manufacturing (HAM) describes the combination of additively built structures onto a conventionally manufactured base body. The advantages of both manufacturing processes are combined in one process chain. As a result, new applications can be achieved with higher cost-effectiveness. With the Additive Manufacturing (AM) process a bonding zone is created that is comparable to a welded joint. In order to evaluate the quality and mechanical properties of the bonding zone, two steels (42CrMo4 and 25CrMo4) are investigated as base body materials with the hot working tool steel X40CrMoV5-1 (AISI H13) for the AM structure. Process parameters for Laser-based Powder Bed Fusion of X40CrMo4V5-1 are developed to achieve a crack and defect free structure as well as an optimized bonding zone in dependency of the base body material. Furthermore, the chemical and mechanical properties are examined in the as-built and heat-treated state. It is observed that a crack-free material bonding is possible and samples with relative densities above 99.5% are obtained. The size of the bonding zone depends on the material of the base body as well as post-process heat treatment. An average hardness of 600 HV1 can be achieved in the “as-built” state.

Thermal Deformation Behavior of Ti-6Mo-5V-3Al-2Fe Alloy

The Gleeble-3800 thermal simulation machine was used to perform hot compression experiments on a new type of β alloy, Ti-6Mo-5V-3Al-2Fe (wt.%), at temperatures of 700–900 °C, strain rates of 5 × 10−1 to 5 × 10−4 s−1, and total strain of 0.7. Transmission and EBSD techniques were used to observe the microstructure. The results show that the deformation activation energy of the alloy was 356.719 KJ/mol, and dynamic recrystallization occurred during the hot deformation. The higher the deformation temperature was, the more obvious the dislocations that occurred and the more sufficient the dynamic recrystallization that occurred, but the effect of strain rate was the opposite. When the deformation temperature was higher than the phase transition point, the recrystallized grains clearly grew up. The calculated strain rate sensitivity index of the alloy was 0.14–0.29. The constitutive equation of hot deformation of Ti-6Mo-5V-3Al-2Fe alloy was established by using the Arrhenius hyperbolic sine equation. The dynamic DMM hot working diagram with the strain of 0.7 was constructed. The relatively good hot working area of the alloy was determined to be the deformation temperature of 700–720 °C and 0.0041–0.0005 s−1.

Effects of W Alloying on the Lattice Distortion and Wear Behavior of Laser Cladding AlCoCrFeNiWx High-Entropy Alloy Coatings

Friction and wear properties of hot working die steel at above 800 °C are of particular interest for high temperature applications. Here, novel AlCoCrFeNiWx high-entropy alloy (HEA) coatings have been fabricated on the surface of hot working die steel by laser cladding. The effects of the as-prepared AlCoCrFeNiWx HEA coatings on the microstructure and high temperature friction and wear behavior of hot working die steel are investigated through scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS). Having benefited from the formation of W-rich intermetallic compounds after the addition of W elements, the high temperature wear resistance of the coatings is obviously improved, and friction coefficient shows a large fluctuation. The microstructural characteristics of the AlCoCrFeNiWx HEA coatings after the high temperature wear resistance test shows a highly favorable impact on microstructure stability and wear resistance, due to its the strong lattice distortion effect of W element on BCC solid solutions and the second phase strengthening of the W-rich intermetallic compounds. These findings may provide a method to design the high temperature wear resistant coatings.

Failures of Tools and Dies

This article discusses failure mechanisms in tool and die materials that are very important to nearly all manufacturing processes. It is primarily devoted to failures of tool steels used in cold working and hot working applications. The processes involved in the analysis of tool and die failures are also covered. In addition, the article focuses on a number of factors that are responsible for tool and die failures, including mechanical design, grade selection, steel quality, machining processes, heat treatment operation, and tool and die setup.

Hot Deformation Behaviors of as Cast 321 Austenitic Stainless Steel

AISI 321 stainless steel has excellent resistance to intergranular corrosion and is generally used in nuclear power reactor vessels and other components. The as-cast and wrought structures are quite different in hot workability, so physical simulation, electron back-scatter diffraction, and hot processing maps were used to study the mechanical behavior and microstructure evolution of as-cast nuclear grade 321 stainless steel in the temperature range of 900–1200 °C and strain rate range of 0.01–10 s−1. The results showed that the flow curve presented work-hardening characteristics. The activation energy was calculated as 478 kJ/mol. The fraction of dynamic recrystallization (DRX) increased with increasing deformation temperature and decreasing strain rate. DRX grain size decreased with increasing Z value. Combining the hot working map and DRX state map, the suggested hot working window was 1000–1200 °C and 0.01–0.1 s−1. The main form of instability was necklace DRX. The nucleation mechanism of DRX was the migration of subgrains. The δ phase reduced the activation energy and promoted DRX nucleation of the tested steel.

Gejala Heat Strain pada Pekerja Pembuat Tahu di Kawasan Kamboja Kota Palembang

Latar belakang: Pabrik tahu merupakan salah satu tempat kerja yang berpotensi menimbulkan iklim kerja panas. Hal ini tidak terlepas dari penggunaan api sebagai media produksi yang dapat menyebabkan seseorang mengalami heat strain. Untuk itu, penelitian ini bertujuan untuk mengetahui proporsi gejala heat strain pada pekerja pembuat tahu dan faktor apa yang paling mempengaruhi gejala heat strain tersebut.Metode: Penelitian ini menggunakan desain cross sectional study dan penetapan sampel menggunakan teknik total sampling. Sampel dalam penelitian ini berjumlah 54 orang yang berasal dari enam pabrik tahu. Analisis data penelitian menggunakan uji chi square untuk analisis bivariat dan uji regresi logistik berganda untuk analisis multivariat.Hasil: Hasil penelitian menunjukkan proporsi gejala heat strain pada pekerja sebesar 64,8% dan diketahui bahwa adanya hubungan antara iklim kerja panas (p-value = 0,008), usia (p-value = 0,014), dan konsumsi air minum (p-value = 0,002) dengan gejala heat strain, dan tidak adanya hubungan antara lama kerja (p-value = 0,077) dengan gejala heat strain. Hasil analisis multivariat menunjukkan bahwa terdapat hubungan antara iklim kerja panas dengan gejala heat strain (p-value = 0,004) setelah dikontrol oleh variabel perancu.Simpulan: Hasil penelitian diketahui bahwa iklim kerja panas merupakan faktor yang paling mempengaruhi gejala heat strain pada pekerja pembuat tahu di Kawasan Kamboja Kota Palembang. Pemilik pabrik tahu dapat melakukan perbaikan ventilasi dan memasang plafon di pabrik, serta menyediakan fasilitas air minum untuk memenuhi kebutuhan air 2,8 liter/hari bagi pekerja. Title: Heat Strain Symptoms in Tofu Production Workers in Kamboja Area of Palembang CityBackground: Tofu industry is one of workplaces which has potential in creating hot working climate. This industry cannot be separated from the use of fire as one of production element where exposure to fire may cause workers to experience heat strain. This study aimed to determine the proportion of heat strain symptoms in tofu workers and what factors most influence the symptoms of heat strain.Method: This study used cross sectional study design and samples were determined by using total sampling technique. Samples in this study amounted to 54 workers from six tofu making businesses. Analysis for study data was using chi-square test for bivariate analysis and multiple logistic regression test for multivariate analysis.Result: The study showed that the proportion for workers with heat strain symptoms was 64.8%. It was found that there was a correlation between hot work climate (p-value = 0.008), age (p-value = 0.014), and water consumption (p-value = 0.002) with heat strain symptoms. Meanwhile, there is no correlation between work length (p-value = 0.077) with heat strain symptoms. The result of multivariate analysis showed that there was a correlation between hot working climate and heat strain symptoms (p-value = 0.004) after control applied from confounding variables.Conclusion: The result showed that the hot working climate was the most influencing factor for the symptoms of heat strain on tofu workers. Tofu factory owners can repair ventilation and install ceilings in the factory. Besides, provide drinking water facilities to meet 2.8 liters/day for workers’ water needs.