0.3-0.06 ~m. The particles were rounded. The dimensions of the region of coherent scattering were 4-6 nm (i.e., the material was ultradispersed diamond). The density determined by pyc- nometer was 3.2 g/cm ~ and with heavy liquids, 3.48 g/cm a. The composition was -90% diamond and -10% adsorbed water, gases and various radicals (which were not completely removed on heating to 900~ in a stream of argon). The ash content was less than i%. Oxidation in air commenced at 350~ After 5 h at 900=C in a sealed copper ampoule, the graphitization was 10%. In 1986, 22 years later, after storage in air at room temperature, the graphitization of the ultradispersed diamond was only 5.7Z, (determined from the loss in weight of three samples, after repeated treatment with H2SO 4 and KNO3). Obviously, the surface energy and the energy defects, due to the small size of the crystals, reduced the thermodynamic meta- stability of the diamond and in the smallest and most defective crystals, very greatly re- tarded the surface graphitization process, even at room temperature.

In conclusion, the authors thank S. E. Saninoy for purifying and analyzing the ultra- dispersed diamond.

LITERATURE CITED

i. A. I. Lyamkin, E. A. Petrov, A. P. Ershov, et al., Dokl. Akad. Nauk SSSR, 302, No. 3 (1988).

2. R. N. Creiner, D. S. Philips, J. D. Johnson, et al , PrepfT~hA~UR 88-I04, Los Almos, USA (1988).

3. A. M. Stayer, N. V. Gubareva, A. I. Lyamkin, Fiz. Goreniya Vzryva, 20, No. 5 (1984). 4. V. F. Petrunin, V. Ya. Pogonin, G. I. Sawakin, et al., Powder Metallurgy, ~ (1984). 5. G. I. Savvakin, V. I. Trefilov, and B. V. Fenochka, Dokl. Akad~ Nauk SSSR, 282, No. 5

(1985). 6. Meider, Theoretical Simulations of Detonation, [Russian translation], Mir, Moscow

(1985). 7. J. Cato, N. Mori, and H. Sakai, in: Eighth Symp. (International) on Detonation, Pre-

print, New Mexico, USA (1985). 8. J. Bante and R. Chirat, ibid. 9. S. A. Gubin, V. V. Odintsov, and V. I. Pepekin, Khim. Fiz., 5, No. 1 (1986).

I0. M. Van Thiel and F. N. Ree, UCRL-Preprint 95839, Livermore, USA (1986).

IMPACT-DIFFUSION WELDING OF METALS

V. F. Sazonov, A. S. Khromov, V. K. Korobov, and S. S. Batsanov

UDC 534.222.2:621.791.18

Diffusion welding is widely used to obtain high-quality welded metal joints, with a strength approaching that of the parent metal [i]. Various physical methods have been used to improve the quality of the weld seam: electromagnetic fields, ultrasonic vibration etc. However, they are all inadequate because the inherent effects are only slight. The method based on explosive action is more promising, since it has a significant action on the struc- ture and the properties of the metals, and as a consequence, on the rate of the diffusion processes [2]. Shock loading has therefore been used to activate the sintering of metallic and ceramic powders [3-5].

The dynamic compression of a metal (in the given case steel 50KhFA) was effected in a multilayer cylindrical vessel, composed of materials of different density. As a source of energy, PVV-4 was used. The impact on the metal created defects, which during subsequent heating, ensured a higher rate of diffusion of the atoms and an improvement of the diffu- sion welding process.

Diffusion welding was effected by submitting the components, after the impact treat- ment, to compression at a pressure, p = 3.3 MPa. Afterwards, the components were heated by induction to 500~ which was maintained for i0 min. The components were then compressed

Mendeleevo. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 3, pp. 125-126, May- June, 1990. Original article submitted September 13, i988; revision submitted January 26, 1989.

368 0010-5082/90/2603-0368512.50 �9 1990 Plenum Publishing Corporation

at a pressure, p = i0 MPa and the temperature raised to 825~ which was maintained for 5 min. The results of mechanical tests on diffusion welded specimens, with preiiminary im- pact treatment (impact diffusion welding) and without it (diffusion welding) are shown in Table i. (a - limiting tensile strength).

If after welding, the specimen was heat treated - hardened at 850~

Temp., ~ Diffusion welding, MPa Impact diffusion welding, MPa

825 734 973 1025 953 1028

annealed in oil at 5200C and then subjected to impact diffusion welding at 1025~ a strength of 1298 MPa was achieved, compared with 1301 MPa for the parent metal. It was therefore pos- sible to achieve a strength equal to that of the main material. The strength achieved by the classical method of welding was only 1125 MPa.

LITERATURE CITED

i. N.F. Kazakov, in: Diffusion Welding of Materials [in Russian], Mashinostroene, Moscow (1976).

2. S.S. Batsanov, I. A. Ovsyannikova, and N. A. Shestakova, Fiz. Khim. Obrab. Mater., No. i, 166 (1974).

3. O. Bergman and J. J. Barrington, J. Am. Ceram. Soc., 49, No. 9, 902 (1966). 4. G.A. Adadurov, O. N. Breusov, G. A. Meerson, et al., Fiz. Khim. Obrab. Mater., No. 5,

140 (1974). 5. E.S. Atroshchenko, E. I. Zharin, and G. A. Fokin, in: Proc. III All-Union Symp. on

Impulse Pressures, [in Russian~, All-Union FTRI Sci. Res. Inst., Moscow (1979).

369