THE INFLUENCE ON Ni-CONTENT ON THE Ms-TEMPERATURE OF Cu-Zn-Al-Ni ALLOYS

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THE INFLUENCE ON Ni-CONTENT ON THE Ms-TEMPERATURE OF Cu-Zn-Al-Ni ALLOYS

N. Mwamba, L. Delaey

To cite this version:

N. Mwamba, L. Delaey. THE INFLUENCE ON Ni-CONTENT ON THE Ms-TEMPERATURE OF Cu-Zn-Al-Ni ALLOYS. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-639-C4-640.

�10.1051/jphyscol:19824102�. �jpa-00221957�

JOURNAL DE PHYSIQUE

CoZZoque C4, suppZdment au n o 12, Tome 43, ddcembre 1982 page C4-639

THE INFLUENCE ON Ni-CONTENT ON THE M,-TEMPERATURE OF C u - Z n - A l - N i ALLOYS

N. ~wamba' and L. Delaey

KathoZieke U n i v e r s i t e i t Leuven, Departement Meetaalkunde, ~ e l g i w n (Accepted 9 August 1982)

Introduction.- Pops (1) and Pops and Ridley ( 2 ) have shown the effect of individual alloying elements upon the transformation temperatures of beta phase Cu-Zn based ternary alloys. From their results, the influence of Ni and A1 (if taken separate- ly) were related to the martensitic transformation temperature as follows :

Ms ( K ) = 3280

-

-

-

On the other hand, Ahlers (3-4) has proposed for Cu-Zn-A1 alloys, the follo- wing general expression for predictory M temperature :

Ms (K) = 2485

-

-

It then results that, to a first approximation, the Ms temperature for Cu-Zn-Ni or Cu-Zn-A1 alloys is a linear function of the zinc and nickel or aluminium con- tents ( 5 ) .

The aim of the present investigation is to determine the effect of addition of both Ni and A1 on martensitic transformation of Cu-Zn I3 phase alloys. Due to tine iarge ar'flnity between Ni and Al, we expect that their combined effect on the stability of the I3 phase will be different from the individual one. At this end, comparison is made between calculated and predicted M following existing relations.

Experimental Procedures.- All alloys, whose composition is shown in fig. 1, were prepared by melting weighted quantities of commercially pure copper, zinc, alumi- nium and nickel in an induction furnace. After casting, sections of ingots were rolled in R-condition to 1 mm thick sheet. Samples of appropriate dimensions cut from sheets were solution treated at 800°C for 15 minutes and then quenched into water or oil at TB > M,, aged at this temperature for one hour and cooled in air to room temperature.

The transformation characteristics were determined by using electrical resis- tivity and dilatometry measurements.

Results and Discussion.- To a first approximation Pops assumes that the change in transformation temperature due to addition of other elements to a Cu-Zn system is additive and suggests the following expression :

But, by comparing measured and predicted Ms following this relation, a great devia- tion is noted. The predicted values are much more higher than the measured one and the discrepancy is as high as 60 to 6 5 O . Compared to the Ms predicted by Ahlers' equations modified with the positive coefficient for Ni taken from Pops, the deviation still exists despite the fact that Ahlers' expression shows a good fit between calculated and measured M in the Cu-Zn-A1 system.

In order to determine the temperature coefficient of nickel more precisely, Cu-Zn-Al-Ni alloys with constant e/a ( = 1,454) and Ni content varying from 0 to 2 atomic % were analysed (nickel is taken with 0.6 as valency conforming to Jones'

+on leave of absence from Universit6 de Lubumbashi, ~a'ire.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19824102

C4-640 JOURNAL DE PHYSIQUE

theory (6)). Based on our own results and using a multiple linear regression, we find the following expression :

M (K) = 3300

-

The temperature coefficient for Ni appears here to be negative rather than the po- sitive one as suggested by Pops. Due to the good agreement between measured and calculated Ms following Ahlers (for Cu-Zn-A1 alloys), one can keep unchanged the zinc and aluminium coefficients and get the following expression :

The constant term and the Ni coefficient change slightly but the latter is still negative.

One can tinus conclude that the difference between Ms predicted by all the relations reported here are appreciable. For this reason one can say that the additive principle suggested by Pops does not prevail here. This can be attributed to the fact that, as said in the introduction, the combined effect of Ni and A1 on the stability of the I3 phase is not a simple cumulation of the individual one (due to great interaction between Ni and Al).

A second reason for large discrepancy between measured and calculated Ms following Pops can be connected to the fact that Pops did not take into account the effect of ageing above Ms prior to measurement contrary to Ahlers. This can explain why the modified Ahlers' linear equation gives good fits with measured M

.

We, therefore, think that this latter expression, is reasonnably good in esti- mating the M temperature.

A T O M I C % A1

Fig. 1 Composition dependence between A1 and Zn contents of all the alloys studied. The numbers marqued on the figure indicate the Ni content in each case. Dashed lines repre- sent the boundary of the R-region at 973 K for tne Cu-Zn-A1 system.

Fig. 2 Measured Ms compared to Ahlers' equation modified as follows :

O C ) = 2481,5

-

Zn + 1,355 at % Al) - 26,73 at % Ni

References.-

1. POPS H., Trans. Met. Soc. AIME

236

2. POPS H. and RIDLEY N., Met. Trans.

1

3. AHLERS M., Scripta Met.

8

4. DELAEY L., Zeit. fiir Metllk.

58

5. DELAEY L. et al., Report 78R1 (1978).

6. MOTT N.F. and JONES H., The theory of Metals and Alloys, Oxford Un. Press (1953)