RESEARCH ELECTRICAL CONDUCTIVITY OF COPPER-CHROMIUM BASED POWDER ALLOY

АBSTRACT

In this work, the electrical conductivity and electrical resistivity of samples of powder alloys based on copper and chromium were investigated. Samples were prepared with a pressing pressure of 400-500 MPa and a sintering temperature of 1100 ^oС. The results showed that the electrical conductivity of the alloy decreases rapidly with an increase in the percentage of chromium, and the electrical resistance increases.

АННОТАЦИЯ

В данной работе были исследованы электропроводность и удельное электрическое сопротивление образцов порошковых сплавов на основе меди и хрома. Были приготовлены образцы с давлением прессования 400-500 МПа и температуре спекания 1100 ^oС. Результаты показали, что электропроводность сплава быстро снижается с увеличением процентного содержания хрома, а электрическое сопротивление увеличивается.

Keywords: Cu-Cr powder alloy, pressing, sintering, electrical conductivity, electrical resistance.

Ключевые слова: порошковой сплав Cu-Cr, прессование, спекание, электропроводность, электрическое сопротивление.   

Introduction

Globally, the demand for efficient powder composite materials for electrodes is growing every day, while the production of electrodes in powder metallurgy and increasing their service life are used in resistance spot welding machines, which are widely used in the automotive industry. In this aspect, the development of effective compositions and technologies for producing copper-based materials produced by powder metallurgy is important, including the characteristics and cost-effectiveness of materials used in the manufacture of electrodes used in resistance spot welding apparatus [1].

A copper-chromium-based composite alloy consists of brittle chromium and plastic particles of copper. Therefore, as a result of increasing pressing pressure and sintering temperature, an increase in density and a decrease in porosity are observed. With an increase in the percentage of chromium, the hardness and tensile strength also increase. A powder composition with a high density is characterized by a high degree of interparticle interaction, which, in turn, improves in the electrical conductivity of the composite material [2-3].

Research Methods

Electrical conductivity and electrical resistivity of samples of copper-chromium-based composite alloy was determined according to requirements given in GOST 15878-70. Samples with a size of 50x5x5 mm were prepared in determination of their electrical conductivity and electrical resistivity (Figure 1).

Figure 1: Samples made of copper-chromium-based composition alloy

The electrical resistance of the samples was determined using a F4104–M1 micrometer. The operation process of the micrometer is based on the measurement of the amount of voltage drop across the measured resistance when a current of a certain value passes through it [4-5].

The F4104-M1 microometer consists of a power supply, current stabilizer, and filter measuring amplifier as well as a synchronization pulse generator.

Specifications of the F4104-M1 micrometer are as follows:

The limits of the permissible values of the basic error from the final value of the measurement range:

4% in range of 1-100 mkOm.

2.5% in range of 0–1 мOм, 0–10 мOм, 0–100 мOм, 0–1 Oм.

1.5 Om in the remaining ranges.

F4104 Micrometer measuring range – from 0-100 mkOm to 0-10 MOm (12 ranges). Accuracy class 1.5; 2.5 and 4 mm² (depending on the measuring range).

According to the analyzed data, the electrical conductivity of copper-chromium-based composite alloy samples was determined by the following formula:

 ,                                                     (1)

Where, R – electrical conductivity of the sample between of potential contacts, Оm;

S – sample surface, mm²;

l_u – distance between potential contacts, mm.

Research Results

We know that the pressing pressure has the greatest effect on the density of a pressed sample of powder composite alloys. For electrical conductivity testing, samples with a pressing pressure of 400-500 MPa and an sintering temperature of 1100 °C were prepared. The temperature in the case when the sintering temperature of the sample is 1100 °C and that is sintering temperature with liquid phase, at this temperature it was possible to obtain the maximum density in all possible ranges of pressing pressure. 

The results of the experiment on the electrical conductivity and electrical resistance of the copper-chromium-based powder alloy are given in Figures 2-3. From these graphs, as a result of the increase in the percentage of chromium in the alloy, the electrical conductivity of the alloy decreases rapidly, and the electrical resistance increases.

∆ - pressing pressure 400 MPa; × - pressing pressure 450 MPa;   - pressing pressure 500 MPa

Figure 2: Effect of chromium content on electrical conductivity of copper-chromium base composite alloy in a state with a sintering temperature of 1100 °C

∆ - pressing pressure 400 MPa; × - pressing pressure 450 MPa;  - pressing pressure 500 MPa

Figure 3: Effect of chromium content on electrical resistivity of copper-chromium base composite alloy in a state with a sintering temperature of 1100 °C

At the same time, the average results obtained in terms of electrical conductivity were observed in samples made of copper-chromium-based powder composite alloy with a chromium content of 1.5-2.0%. From the graphs obtained in Figures 2, it was found that the electrical conductivity of copper-chromium-based powder composite alloys with a chromium content of 1.5-2.0% gives 70-86% of the electrical conductivity of pure copper.

Conclusion

Given the results obtained in terms of the electrical conductivity of the copper-chromium-based composition alloy, as well as the mechanical properties of the same alloy, it was concluded that the optimum amount of chromium should be 2% in the case when the chemical composition of the developed composition powder alloy has a pressing pressure of 450MPa and a sintering temperature of 1100 °С.

References:

1. Williams, B., Powder metallurgy – a global market review. In International Powder Metallurgy Directory & Yearbook, 13th edn 1, 2008/2009, pp. 5–14.
2. Claudiu Nicolicescu, M. Miclău, V.H. Nicoară. Wear Behavior of Materials Based on Cu/Cr and Cu/Cr/W used for Welding Electrodes”. “Web of Scientist: International Scientific Research Journal” Vol. 36, No. 4 (2014) 348-353.
3. H. Huh and W. Kang, “Electrothermal analysis of electric resistance spot welding processes by a 3-D finite element method,” Journal of Materials Processing Technology, vol. 63, no. 1–3, pp. 672–677, 1997.
4. А. Kh. Alikulov, U.N. Ruziev, F. Mengaliyev “Аnalysis of materials for contact spot welding electrodes”. “International Journal of Discoveries and Innovations in Applied Sciences (IJDIAS) ISSN 2792-3983” India. 2022 (12), Р.13–16. 
5. А.Kh. Alikulov, B.Sh. Bektemirov, F.R. Norkhudjaev, Z.B. Mirzarakhimova. Determination of  Density of  The Samples Made of Copper Based Materials // Best journal of innovation in science, research and development. ISSN: 2835-3579 volume:02 issue: 09/2023 P. 106-111.