Strength properties and structure of CuCrZr alloy subjected to low-temperature KOBO extrusion and heat treatment

Paweł Ostachowski,Marek Łagoda,Włodzimierz Bochniak,Stanisław Ziółkiewicz

doi:10.1007/s00170-019-04602-4

Abstract

KOBO extrusion of metals and alloys strongly activates the point defect generation processes, as a result of which they reach a concentration exceeding the equilibrium level by many orders of magnitude. This leads to significant acceleration of diffusion phenomena which in heat-treatable alloys may cause disturbance of the thermodynamic equilibrium between the solid solution decomposition and dissolution of precipitates. In this work, measurements of mechanical and electrical properties and structural observations Cu1Cr0.1Zr alloy subjected to low-temperature KOBO extrusion at different stages of multi-variant heat treatment were conducted. In addition, the geometry of the extruded alloy’s flow zone was analyzed and the obtained results made it possible to assess the effectiveness of experimental procedures, including product formation with high extrusion ratio λ, aimed at achieving of high and thermally stable functional properties of the material.

Highlights

Age-hardenable CuCrZr alloys achieve high functional properties thanks to the application of heat or thermomechanical treatment
Coarse chromium particles generated during solidification, particles not dissolved during solution annealing, and chromium-rich particles precipitated during aging were identified in Cu1Cr.01Zr alloy subjected to heat treatment [7]
The results of the first series of tests, concerning hardness, specific electrical conductivity, and initial structure of CuCrZr alloy in commercial temper and of the products in the form of Ø12-mm rods extruded from it (Fig. 2), using the KOBO method at temperature ranging from 200–300 °C, are given in Table 1 and in Figs. 3, 4, 5, 6, 7, and 8

Summary

Introduction

Age-hardenable CuCrZr alloys achieve high functional properties thanks to the application of heat or thermomechanical treatment. Due to a favorable combination of strength properties, as well as electrical and thermal parameters, the alloy can be classified as one of the so-called functional materials used for various applications, mainly in the production of high heat flux components of ITER (International Thermonuclear Experimental Reactor), and in the manufacturing of trolley contact wire dedicated for high-speed trains on electrical railways, resistance welding electrodes, and electronic commutators [1,2,3]. Coarse chromium particles generated during solidification, particles not dissolved during solution annealing, and chromium-rich particles precipitated during aging were identified in Cu1Cr.01Zr alloy subjected to heat treatment (supersaturation, 1000 °C/1 h, and subsequent aging, 480 °C/5 h) [7]. The fact that CuCrZr alloy owes its high strength properties due to fine, chromium-rich particles formed during aging of previously supersaturated alloy is confirmed by a series of studies. The following particles have been identified: Cu4Zr and CrCu2(Zr) [8,9,10]; Cu51Zr14 [11]; Cr, Cu5Zr, and Cu [10, 12, 13]

Methods

Results

Conclusion