M I K H A I L Y U L ' E V I C H B A L ' S H I N - S I X T I E T H B I R T H D A Y

A. S. F i a l k o v

Translated from Poroshkovaya Metallurgiya, No. 4(16), pp. 3-5, July-August, 1963

On October 5, 1963, Mikhail Yul 'evich Bal ' sh in-one of the pioneers and most prominent workers in powder meta l lurgy-ce lebra ted his sixtieth birthday. His publications in the field of powder metallurgy (numbering about fifty) are widely known and recognized both at home and abroad. M. Yu. B al 'shin's books have for long been accepted as students' textbooks.

One of the first works by Barshin was the book "Metal Ceramics," published in 1988. It presented a number of fundamental principles of com- pacting and sintering of powders, which even today are widely referred to in the Soviet and foreign scientific literature. This monograph was the first to provide a basis for the theory dealing with the character of the metal powder shaping processes and for the fact that, in compacting and sintering, the bond rupturing processes between particles are as important as the bond forming processes. At one time, this view gave rise to controversy. Today, it is gen- erally accepted.

In "Metal Ceramics," Bal'shin also for the first time demonstrated the rote of the elastic relaxation phenomena during the compacting and sinter- ing of powder materials and described a number of important regularities of

the compacting of metal powders (linear density decrease along the compact height, formula for the variation of pressure with height, formulas relating compacting pressure with density).

A major part in the development of metal powder science was also played by.two other studies by Bal'shin, namely, "Powder Metallography" and "Powder Metallurgy." In these, the author for the first time introduced the all-important concept of the contact section of powder materials and proposed a method of determining the mag- nitude of this section, consisting in obtaining the ratio of the modulus of elasticity of the porous mater ia l to the- modulus of elasticity of the corresponding dense material. Today, it would be difficult to visualize the develop- ment of the modern theory of shaping and properties of powder materials without the concept of the contact section. In the same monographs, the knowledge of elastic relaxation was further expanded. In particular, it was shown that the role of elastic relaxation increases with increasing hardness of the metal being compacted and it was demon- strated that the magnitude of the elastic relaxation of powder materials depends but very slightly on compacting pressure.

In "Powder Metallography," sintering was considered for the first time as a quantitative and qualitative change in the contact between particles, brought about by the thermal mobility of atoms. The same study was the first to establish the very important phenomenon of zonal segregation during sintering, consisting in growth of particle con- tact surface and decrease of porosity in some sections (zones) of the part being sintered, and reduction of contact surface and increase of porosity in other sections.

On the basis of theoretical calculations, Bar shin [2, 4] put forward the hypothesis that the Poisson's ratio of powder materials increases as their porosity decreases. Experiments carried out lately by various authors confirmed the validity of this hypothesis. Bal'shin's other studies, published during the last 15 years, are also of interest. Thus, in [5], an exponential relationship was established for the first time between values of relative density & and contact section a:

6~ ~ ~t 'rt

together with a corresponding exponential relationship between contact properties (modulus of elasticity E, tensile strength o b, etc.):

259

~bp,'Vbd~ ~m,

where ~bp and Obd are % values of the porous and dense metals, respectively. It was established by Bal'shin [5, 6] that the l imi t ing value of m for c~ and o b at the maximum ~equil ibrium" value of contact section is 3. Bal'shin's formula is of considerable prac t ica l significance, since it enabled for the first t ime the maximum attainable strength

ceil ing" in the manufacture of porous metals to be determined easily and accurately.

In ['6, 7], Barshin demonstrated that, when powders of the same meta l , having the same hardness but differ- ent in i t ia l porosities, are subjected to compact ing or cold densification by tapping, the same decrease of porositiy will take p lace if the compact ing pressure (or tapping conditions) is the same.

A series of interesting studies by Bal 'shin was published in the collect ions "Investigations of Heat-Resisting Alloys ~ [8, 9, 10, 11]. Work [8] was devoted to a model study of sintering, based on the kinetics of variation of an impression contact section under a constant load applied to an indenter. With this method, it is possible to estab- lish a strict relationship between deformation kinetics during sintering and the magnitude of applied stress, which

could not be done by the method of model study of sintering, proposed by the American investigator D. Kuczynski. It was found by Barshin that deformation consists of a rapid plastic strain and a slow quasiviscous flow.

New principles of ca lcula t ing the rate of closing up of pores were presented in [9]. It was shown that the rate values obtained by ear l ier calculat ions were excessive by more than one order of magnitude.

In [6, 11], Bal'shin developed the idea of unity between different regularit ies of compact ing and sintering, with the aid of which it was possible to ca lcula te the kinetics of variation of contact properties (strength, modulus of e las t ic i ty) and shrinkage during sintering under pressure. It was shown that a linear relationship exists between the square of the value of contact properties and holding t ime.

A number of investigations into sintering under pressure were carried out by Bar shin in collaborat ion with his pupil , A. A. Trofimova [12, 13, 14]. These studies revealed some new relationships character izing sintering under pressure, such as the approximate ly inverse proport ionali ty between holding t ime and sintering rate, independence

of the shrinkage rate of fine powders at equal holding t imes on sintering temperature, etc.

Of interest is Bal 'shin's paper, published in this issue, to the Sixth Al l -Union Conference on Powder Metallurgy, deal ing with the exper imenta l de terminat ion of contact section and contact properties. In this study, contact sec- t ion was determined from the ratio of the moduli of e las t ic i ty of porous and dense metals. The investigaton demon- strated that, at smal l loads, stresses are almost ent i rely concentrated within a part of the nominal section, equal to

the contact section.

Bar shin first developed an essent ial ly new method of preparation of powder metals, consisting in the aggre- gation of meta l powders prior to shaping. This method was subsequently e laborated by other Soviet specialists, V. I.

Likhtman, I. S. Brokhin, G. V. Samsonov, and G. A. Meerson.

Bal'shin took an act ive part ( together with B. A. Borok and N. A. Gavrilov) in developing the technology of. planning, and putting in commission the first copper powder production plant in the USSR, development of porous

iron-base bearings, etc.

Bal'shin has trained a large number of specialists, both engineers and scientists, who are ac t ive ly part icipat ing

in the further development of powder meta l lurgy in our country.

L I T E R A T U R E C I T E D

1. M. Yu. Barshin, Metal Ceramics [in Russian], Moscow, Metal lurgizdat (1938). 2. M, Yu. Bal'shin, Powder Metal lography [in Russian], Moscow, Metal lurgizdat (1948). 3. M. Yu. Bal'shin, Powder Meta l lu rgy[ in Russian], Moscow, Mashgiz (1948). 4. M. Yu. Bal'shin, "Technology of preparation of sintered parts, ~ in Handbook: Mechanical Engineering [in

Russian], Moscow, Mashgiz, Vol. 6 (1947). 5. M. Yu. Bal'shin, Doklady Akad. Nauk SSSR, 6_..77, 831 (1949). 6. M. Yu. Bal'shin, Paper to Conference on Powder Metallurgy, Collect ion: Powder Metal lurgy [in Russian], Mos-

cow, Metal lurgizdat (1954). 7. M. Yu. Bal'shin, "Progress in powder metal lurgy," Collect ion: Principles of Metal lurgy [in Russian], Moscow,

Metal lurgizdat (1961), Vol. 1, Part 2, p. 343. 8. M. Yu. Bal'shin, Col lect ion: Investigations of Heat-Resisting Alloys [ in Russian], Moscow, Akademkniga (1960),

Vol. 2, p. 359.

260

9.

I0.

11.

12.

13.

14.

15.

M. Yu. (1960),

M. Yu. Vol. 4.

M. Yu. (1962), M. Yu. M. Yu. M. Yu. (1961). M. Yu.

Bal' shin, Col lect ion:

Vol. 6.

Bal' shin, Col lect ion:

Investigations of Heat-Resisting Alloys [in Russian], Moscow, Akademkniga

Investigations of Heat-Resisting Alloys [in Russian], Moscow, Akademkniga (1959),

Bal'shin, Col lect ion: Investigations of Heat-Resisting Alloys [in Russian], Moscow, Akademkniga Vol. 7. Bal'shin and A. A. Trofimova, Poroshkovaya Met., I, 82 (1961). Bal'shin and A. A. Trofimova, Poroshkovaya Met., 1, 102 (1962). Bal 'shin and A. A. Trofimova, Izvest. Akad. Nauk SSSR, Otdel. Tekh. Nauk, Met . i Topliv• 6, 45

Bal'shin, Poroshkovaya Met., 4 (1963).

All abbreviations of periodicals in the above bibliography are letter-by-letter transliter- ations of the abbreviations as given in the original Russian journal. Some or all of this peri- odical l i terature may well be available in Engl i sh translation. A complete List of the cover-to. cover English translations appears at the back of this issue.

261