PENGARUH HOLDING TIME DAN MEDIA PENDINGIN PADA CARBURIZINGMATERIAL SUS 630 TERHADAP NILAI KEKERASAN DAN STRUKUR MIKRO

Stainless steel is material that mostly used in chemical industry because of its excellence in corrosion resistance, in addition to corrosion resistance, hardness on the surface of the material it is also be considered, to meet these needs material engineering is carried out, which is surface hardening. Carburizing is one method to harden the surface. This study aims to determine the effect of holding time and cooling (water, air, and oil) on carburizing SUS 630 stainless steel to hardness, microstructure, and diffusion depth. The material used is SUS 630 stainless steel, with carbon content 0.02%. The heating process at temperature 1020°C with holding time 1 hour, 2 hours, 3 hours, 4 hours and 5 hours then cooled to water, oil and air cooling. Test results show; 1) the longer holding time the value of hardnesswill increases. The maximum hardness value is at 5 hours holding time are 76HRN(water), 71.4HRN(air), and 78.2HRN(oil); 2) the occurrence of micro structure transformation due to holding time and cooling. The microstructure formed is structure of ferrite, perlite and martensite; 3) the longer holding time, the diffusion depth will increases. The maximum diffusion depth value is 5 hours holding time are 7.55ɥm(water), 10.42ɥm(air), and 9.98ɥm(oil). Keywords : Carburizing, Diffusion, Holding Time, Hardness, Microstructure.

Dynamics and healing behavior of metallosupramolecular polymers

Self-healing or healable polymers can recuperate their function after physical damage. This process involves diffusion of macromolecules across severed interfaces until the structure of the interphase matches that of the pristine material. However, monitoring this nanoscale process and relating it to the mechanical recovery remain elusive. We report that studying diffusion across healed interfaces and a correlation of contact time, diffusion depth, and mechanical properties is possible when two metallosupramolecular polymers assembled with different lanthanoid salts are mended. The materials used display similar properties, while the metal ions can be tracked with high spatial resolution by energy-dispersive x-ray spectrum imaging. We find that healing actual defects requires an interphase thickness in excess of 100 nm, 10 times more than previously established for self-adhesion of smooth films of glassy polymers.

Multi-term time fractional diffusion equations and novel parameter estimation techniques for chloride ions sub-diffusion in reinforced concrete

In this paper, searching for a better chloride ions sub-diffusion system, a multi-term time-fractional derivative diffusion model is proposed for the description of the time-dependent chloride ions penetration in reinforced concrete structures exposed to chloride environments. We prove the stability and convergence of the model. We use the modified grid approximation method (MGAM) to estimate the fractional orders and chloride ions diffusion coefficients in the reinforced concrete for the multi-term time fractional diffusion system. And then to verify the efficiency and accuracy of the proposed methods in dealing with the fractional inverse problem, two numerical examples with real data are investigated. Meanwhile, we use two methods of fixed chloride ions diffusion coefficient and variable diffusion coefficient with diffusion depth to simulate chloride ions sub-diffusion system. The result shows that with the new fractional orders and parameters, our multi-term fractional order chloride ions sub-diffusion system is capable of providing numerical results that agree better with the real data than other models. On the other hand, it is also noticed from the numerical solution of the chloride ions sub-diffusion system that setting the variable diffusion coefficient with diffusion depth is more reasonable. And it is also found that chloride ions diffusion coefficients in reinforced concrete should be decreased with diffusion depth which is completely consistent with the theory. In addition, the model can be used to predict the chloride profiles with a time-dependent property. This article is part of the theme issue ‘Advanced materials modelling via fractional calculus: challenges and perspectives’.

Coupled Multifield Response to Coordinate Mining of Coal and Uranium: A Case Study

The coordinate mining of stack resources in the Ordos Basin, which involves the coupling effects of stress fracture, seepage, and reactive solute transport, plays an important role in resource exploration and environment protection. A coupled multiphysical–chemical model, involving a modified non-Darcy flow model, a leaching solution reaction, and a reactive solute transport model, was developed in this study. The Fast Lagrangian Analysis of Continua -Computational Fluid Dynamics (FLAC3D-CFD) simulator coupled with the developed models was used to investigate the evolution and morphology of mining-induced multifield coupling for the scenarios of concurrent mining and asynchronous mining of coal and uranium. As mining advanced to 160 m, the maximum principle stress characterized by a stress shell was observed. As mining progressed to 280 m, a rupture occurred, and a new stress shell was generated as a rear skewback was formed by the concentrated stress of the stope. An “arch-shaped” fracture field combined with a “saddle-shaped” seepage field was identified in the destressed zone of the stress shell. In the coordinated mining of uranium prior to coal, “funnel-shaped” and “asymmetric saddle-shaped” morphologies of the leaching solution were found during coal mining for ventilation in the stope and mining face. By contrast, “saddle-shaped”, “inclined funnel-shaped”, and “horizontal” morphologies of the leaching solution were observed for a short period for ventilation of the stope and mining face for coal mining prior to uranium mining, uranium mining prior to coal mining, and synchronized coal and uranium mining. A dynamic stress response was obtained in the coal seam, followed by the conglomerate aquifer and the uranium deposits. The diffusion depth of the solution was negatively correlated with the injection velocity and the pumping ratio and positively correlated with the diffusion coefficient. A dynamic increase in diffusion depth was observed as the diffusion coefficient increased to 1 × 10−4 m2/s.

Effect of Adjusted Gas Nitriding Parameters on Microstructure and Wear Resistance of HVOF-Sprayed AISI 316L Coatings

Gas nitriding is known as a convenient process to improve the wear resistance of steel components. A precipitation-free hardening by low-temperature processes is established to retain the good corrosion resistance of stainless steel. In cases of thermal spray coatings, the interstitial solvation is achieved without an additional surface activation step. The open porosity permits the penetration of the donator media and leads to a structural diffusion. An inhomogeneous diffusion enrichment occurs at the single spray particle edges within the coating’s microstructure. A decreasing diffusion depth is found with increasing surface distance. The present study investigates an adjusted process management for low-temperature gas nitriding of high velocity oxy-fuel-sprayed AISI 316L coatings. To maintain a homogeneous diffusion depth within the coating, a pressure modulation during the process is studied. Additionally, the use of cracked gas as donator is examined. The process management is designed without an additional surface activation step. Regardless of surface distance, microstructural investigations reveal a homogeneous diffusion depth by a reduced processing time. The constant hardening depth allows a reliable prediction of the coatings’ properties. An enhanced hardness and improved wear resistance is found in comparison with the as-sprayed coating condition.

Modeling the Kinetics, Dynamic Profiles and Strategies for Optimal Efficacy of Photo-Polymerization in Thick Polymers

The kinetics and optimal efficacy conditions of photoinitiated polymerization are theoretically presented. Analytic formulas are derived for the crosslink time, crosslink depth and efficacy function. The roles of photosensitizer (PS) concentration, diffusion depth and light intensity on the polymerization spatial and temporal profiles, for both uniform and non-uniform cases, are presented . For optimal efficacy, a strategy via controlled PS concentration is proposed, where re-supply of PS in high light intensity may achieve a combined-efficacy similar to low light intensity, but has a much faster procedure. A new criterion of efficacy based on the polymerization (crosslink) [strength] and [depth] is introduced.