Borosilicate Glass-Ceramics Containing Zirconolite and Powellite for RE- and Mo-Rich Nuclear Waste Immobilization

In order to increase the loading of rare earth- and molybdenum-rich high-level waste in the waste forms, zirconolite- and powellite-based multi-phase borosilicate glass-ceramics were synthesized via an in-situ heat treatment method. The effects of the CTZ (CaO, TiO2 and ZrO2) content on the crystallization, microstructure and aqueous durability of the multi-phase borosilicate glass-ceramics were studied. The results indicate that the increase of CTZ content can promote crystallization. The glass-ceramics presented even structures when the CTZ content was ≥ 40 wt%. For the glass-ceramic with 40 wt% CTZ, only zirconolite and powellite crystals were detected and powellite crystals were mainly distributed around zirconolite, whereas for the glass-ceramics with 50 wt% CTZ, perovskite was detected. Furthermore, the leaching rates of Na, Ca, Mo and Nd were in the ×10−3, ×10−4, ×10−3 and ×10−5 g·m−2·d·−1 orders of magnitude on the 28th leaching day, respectively.

Austempering and Bainitic Transformation Kinetics of AISI 52100

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.

A Study of the Influence of Local Heat Treatment on the Structure of Welded Titanium Pipelines

The article analyzes the results of a study of the influence of zonal heat treatment on the structure of welded joints of pipeline elements made of titanium alloys Ti-3.5Al-1.5Mn. In the manufacture of such structures, the TIG welding method is used to join pipe elements, after which the heat treatment method can be used to relieve residual stresses. The experiments have confirmed the effectiveness of zonal heat treatment preceded by welding. It was revealed that for welded joints made of titanium alloys, heat treatment can stabilize the structure. In experiments conducted by the method of optical metallography, the structure of heat treated and untreated welded joints was investigated. The influence of heat treatment on the weld structure and heat-affected zone was identified.

Effect of Heat Treatment on Microstructure and Mechanical Properties of AlSi10Mg Alloy Fabricated by Selective Laser Melting

The effects of the heat treatment process parameters on the microstructure and mechanical properties of a selective laser melted (SLMed) AlSi10Mg alloy were systematically investigated. The SLMed AlSi10Mg alloy was treated with T1 (180°C× 4h + air cooling) process, which had the microstructure of fine α-Al grains, fine Si phase, and nano-sized precipitations. The microhardness significantly increased to 150 HV, which is even higher than as-SLMed one (126 HV). The microhardness of SLMed AlSi10Mg alloy treated with T4 (540°C × 2h + water cooling) heat-treatment process significantly decreased to 62 HV due to the growth of α-Al grains, Si phase and the formation of β-AlFeSi phase. However, the microhardness and ultimate tensile strength of AlSi10Mg alloy treated with T6 (540°C × 2 h water cool + 180°C × 4 h air cool) process decreased to 91 HV, although the strengthening precipitation of Mg2Si phase formed. It indicates that the Mg2Si phase cannot compensate for the adverse effect of grain growth. It may provide the best potential heat treatment method for fabricating the high strength SLMed AlSi10Mg alloy.