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The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs of 4 units represent different material conditions as follows: • Irradiated (Unit 4), • irradiated and recovery annealed (Units 2 and 3), and • irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam. Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. This report presents test results measured on the trepans from the beltline welding seam No. SN0.1.4. and forged base metal ring No. 0.3.1. of the Units 1 2 and 4 RPVs. The key part of the testing is focussed on the determination of the reference temperature T0 of the Master Curve (MC) approach following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined: • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed. • KJc values of the weld metals generally followed the course of the MC though with a large scatter. • There was a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. • The T0 measured on T-S oriented SE(B) specimens from different thickness locations of the welding seams strongly depended on the intrinsic structure along the crack front. • The reference temperature RT0 determined according to the “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs - VERLIFE” and the fracture toughness lower bound curve based thereon are applicable on the investigated weld metals. • A strong scatter of the fracture toughness KJc values of the recovery annealed and re-irradiated and the irradiated base metal of Unit 1 and 4, respectively is observed with clearly more than 2% of the values below the MC for 2% fracture probability. The application of the multimodal MC-based approach was more suitable and described the temperature dependence of the KJc values in a satisfactory manner. • It was demonstrated that T0 evaluated according to the SINTAP MC extension represented the brittle fraction of the data sets and is therefore suitable for the nonhomogeneous base metal. • The efficiency of the large-scale thermal annealing of the Greifswald WWER 440/V230 Unit 1 and 2 RPVs could be confirmed.

No description available.

No description available.

No description available.

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The area of research dealing with joining of dissimilar metals has been active in recent time. Although fusion and non-fusion techniques of joining have been effectively used for manufacturing components, a comprehensive scientific understanding of the process is lacking. This void exists both in fusion and non-fusion welding methods. The present investigation addresses some of these aspects. The investigation consists of two sections - Part A and Part B. Part A is on Friction welding and Part B deals with Fusion welding using laser. Each section has two chapters each. Following an introductory chapter, basic aspects of friction welding is presented in chapter 2. Chapter 3 deals with the work on friction welding of Fe-Cu couple. Fe-Cu couple is a system with positive heat of mixing. After a brief introduction on various non-equilibrium processes that can occur in this system, experimental details and results are presented. Using the results an attempt is made to understand the flash formation, formation of pores at the interface and the formation of chemically altered zone. It is observed that a chemically altered layer forms predominantly on the Cu side of the interface. It consists of Fe entrapped as fragments/fine crystals and as solid solution in Cu matrix. This zone has higher thickness at the edges than at the center. The mechanism of formation of this interfacial layer which is central to the joining process is related to the fracture and transport of fragments during plastic deformation. Fe forms solid solution in copper under non-equilibrium conditions promoted by shear energy. Using the concept of ballistic mixing, the formation of solid solution is explored. Using nano-indentation experiments mechanical properties of the weldment is estimated and an attempt is made to correlate mechanical properties with the amount of second element present in that location. The chapter 4 in part A deals with the friction welding of Ni-Ti couple. Ni-Ti system has negative heat of mixing and it forms a number of intermetallics. After a brief introduction to the chapter, various experimental techniques and strategies followed to carry out the experiments are explained. Following these, the results are presented. It is observed that TiNi3 formed at initial stage. Theories based on effective heat of formation and surface energy also predict the nucleation of TiNi3. With the continuation of frictional processes, the formation of TiNi and Ti2Ni phases were also observed. Formation of Ti2Ni was shown to greatly accelerate due to shear process. In this system two complementary processes like ballistic mixing and thermal assisted diffusion accelerate Ti2Ni formation. From mechanical tests it is found that Ti2Ni layer in the weldment is weak and hence formation of Ti2Ni in the weldment is detrimental. In chapter 5 an introduction to fusion welding of dissimilar metals is presented as background materials for the subsequent chapters. Chapter 6 deals with nature of segregation of Ag during laser welding of Fe-Ni couple. Ag is used as a tracer to probe fluid flow in the Fe-Ni couple during laser welding. Ag is immiscible both in Fe and Ni whereas Fe and Ni form a complete solution at an elevated temperature and in liquid state. Besides the experimental work, numerical simulation of the weld pool were carried out using homogeneous mixture model using SIMPLER algorithm. Experiments and simulations indicate that fluid flow is asymmetrical and in the deep penetration welding strong convection in the pool drives the tracer to the top of the pool. Overall distribution of the tracer is due to the combined effect of convection and diffusion. In shallow welding there exists a boundary region where tracer does not penetrate. In chapter 7 the results of instrumented indentation experiments on laser welded Fe-Cu weldment has been presented. It was earlier reported that during laser welding of Fe-Cu couple, a variety of microstructures evolves at various locations in the weldment and hardness of the weldment were found to be very high. Here an attempt has been made to explore in details the origin of such a high hardness. The chapter starts with a description of various microstructures that are observed in this weldment followed by the various procedures used for extracting data from instrumented indentation tests. It is followed by the presentation of the experimental results. It is found that rule of mixture along with Hall-Petch strengthening explains the observed increase in hardness of the weldment. The fine scale microstructure consisting of alternate Fe rich and Cu rich layers increases the hardness of the weldment. On copper side of the weldment, composition and scale of microstructure fluctuates and so also the hardness. Finally in chapter 8 overall conclusions of the various chapters in the thesis have been summarised.

Friction bit joining (FBJ) is a new solid-state spot joining technology developed in cooperation between Brigham Young University of Provo Utah, and MegaStir Technologies of West Bountiful Utah. Although capable of joining several different material combinations, this research focuses on the application of FBJ to joining 5754 aluminum to DP 980 steel, two alloys commonly used in automotive applications. The thicknesses of the materials used were 0.070 inches (1.78 mm) and 0.065 inches (1.65 mm), respectively. The FBJ process employs a consumable 4140 steel bit and is carried out on a purpose built research machine. In the first stage of the weld cycle the bit is used to drill through the aluminum top sheet to be joined. After this, spindle speed is increased so that the bit tip effectively forms a friction weld to the steel bottom sheet. Momentary stoppage of the spindle facilitates weld cooling before the spindle is restarted, shearing the bit tip from the bit shank, and retracted. Incorporated into the bit tip geometry is a flange that securely holds the aluminum in place after joint formation is complete. This research consists of several developmental steps since the technology only recently began to be formally studied. Initial joint strengths observed in lapshear tensile testing averaged only 978.5 pounds (4.35 kN), with a relatively high standard deviation for the data set. Final lapshear tensile test results were improved to an average of 1421.8 pounds (6.32 kN), with a significantly lower, and acceptable, standard deviation for the data set. Similar improvements were realized during the development work in cross tension tensile test results, as average strengths increased from 255.8 pounds (1.14 kN) to 566.3 pounds (2.52 kN). Improvements were also observed in the standard deviation values of cross tension data sets from initial evaluation to the final data set presented in this work.