Volume 62, Issue 6

With good electrical conductivity and high ultimate strength and yield strength limit, copper-beryllium alloy is widely used in springs and electrical contacts. This article studies the effect of heat treatment on microstructure, precipitation process, and mechanical properties of beryllium copper alloy C17000 from a 0.3 mm thick sheet. The results show that the average HB hardness and strength of sample material after tempering at 800 °C for 0.5 h and water quenching are about 100 HB and 300 MPa, respectively. The sample after quenching and aging at 400 °C for 1 hour has a hardness up to 400 HB and a strength of up to 1200 MPa; both the hardness and strength after age hardening of samples are about 4 times higher than the sample after quenching. The increase in strength is caused by the irregular precipitation process of the gamma phase in the form of spheres in grains and grain boundaries, in the form of bands at grain boundaries and twin boundaries.

The microstructural evolution and tensile properties of Mg-4Zn-0.5Y-0.5Nd-0.3Zr alloy were studied after casting, hot extrusion, and solution treatment. The as-cast alloy features coarse grains and a semi-continuous skeletal W’ phase. Hot extrusion induces dynamic recrystallization, forming refined equiaxed grains and aligning fragmented second-phase particles along the extrusion direction (ED), significantly enhancing yield tensile strength (YTS), ultimate tensile strength, and elongation by 229 %, 119 %, and 50 %, respectively. Solution treatment (420–500 °C, 3–8 h) dissolves coarse phases, promotes fine precipitate formation, and causes grain coarsening. Optimal properties are achieved at 460 °C for 5 h, yielding a 32 % increase in YTS due to grain refinement, texture, solution, and precipitation strengthening.

The aim of this work is to study the micro-structural variations of 2205 duplex stainless steel welded by the gas metal arc welding (GMAW) process in three transfer modes: spray transfer, globular transfer and dip transfer. Duplex stainless steels, characterized by a two-phase microstructure of austenite and ferrite, exhibit exceptional mechanical properties and corrosion resistance that can be significantly affected by welding techniques. Plates of 8 mm thickness, solution annealed at 1100 °C, were joined using ER 2209 welding wire and a shielding gas mixture of 98 % Argon and 2 % O 2 . Various welding parameters were optimized to maintain an interpass temperature below 100 °C and a heat input ranging from 0.38 to 1.20 kJ/mm. The microstructure was prepared and etched with KOH reagent and analyzed by optical microscopy. The results show that all welding modes resulted in a significant increase in ferrite content within the heat affected zone (HAZ), with the spray mode exhibiting the highest delta ferrite and a coarsened microstructure due to elevated temperatures and slow cooling rates. In the weld region, spray mode contains the highest amount of austenite phase and exhibits distinct morphologies including grain boundary austenite (GBA), Widmanstätten austenite (WA) and intergranular austenite (IGA). The lowest amount of austenite is found in the weld metal of the dip transfer mode.

Clamp strips, a.k.a. fixation bands or tack strips (Schellenbänder) are used to fix instrumentation wires in turbomachinery to components where sensors are installed for instrumentation and control (I&C). Some of said tack strips fractured in a test engine installation. They were received at the authors’ laboratory for a metallurgical root cause failure investigation. For comparison, wide and narrow new, unused clamp strips were also received. All fractured tack strips were metallographically sectioned. They all exhibited an unfavorable banded micro-structure with cerium carbide, and/or cerium oxide, and/or titanium carbonitride inclusions. Even though these inclusions may have contributed to the premature overload failures of the tack strips due to their lowering the fracture ductility, they were not causative for the failures. The root cause of the overload failures was abusive use in the installation process. Too many instrumentation wires were fixed with the subject tack strips at the same time, causing mechanical overload of the very thin, non-high strength strips made of nickel-base, solid solution strengthened heat conductor alloys. It is important to note that the spot welds used to fix the tack strips were unrelated to the failures, even though some of the overload cracks propagated through spot weld nuggets.