Investigation of the Ni3Al-Fe alloys by resistivity measurements and differential thermal analysis

Abstract

The Ni 3 Al based intermetallic compound (γ' phase) is the main strengthening phase of foundry heat resistant nickel alloys, which represent an important group of high strength materials used when fabricating the most important details of gas turbine motors [1,2]. Currently the VKNA type alloys based on the Ni 3 Al compound (90% intermetallic phase) are developed and used in industry [3].The Ni 3 Al is ordered according to type L1 2 and occurs in a narrow concentration range near 25 at % Al. Its feature is the ability to dissolve almost all transition elements in various combinations. Substitutional alloying of this alloy extends the occurrence region of the γ' phase [2] and leads to a substantial variation in the character and temperature ranges of phase and structural transformations in the Ni 3 Al-X system [4].Practical application as a heat resistant construc tion material requires the elimination of the intercrys tallite brittleness, which is inherent to the Ni 3 Al alloy in the polycrystalline state. Iron is considered a possi ble plastificator [5].Ni 3 Al-Fe alloys are of interest for investigation not only from the manufacturing viewpoint, but also from the physical one. The solubility of iron in γ' phase sub stantially depends on the ratio of atomic concentra tions of nickel and aluminum. The chemical activity of iron and nickel atoms is close, and iron is able to form the Ni 3 Fe intermetallic phase. All these factors lead to the iron atoms being able to substitute the sites of both nickel and aluminum atoms [2]. From this viewpoint, the Ni 3 Al-Fe system can serve as the model system for the Ni 3 Al based alloyed alloys.The Ni 3 Al intermetallic compound has a high degree of long range order close to unity and retaining upon heating to 1330°C. Above this temperature, dis ordering starts. The temperature of complete disorder ing (t k ) is not attained in the solid state for the stoichi ometric alloy (Ni 75 Al 25 ). However, alloying with tran sition elements such as iron, chromium, and manganese promotes the transition from intermetallic properties to the properties of the ordering alloy as their concentration increases: quantity t k can be detected in the solid state [6].As a rule, electron scattering at lattice inhomoge neities in the solid solution decreases upon its order ing. Resistivity (ρ) is lower in the ordered region, while a decrease in the degree of long range order S is accompanied by an increase in ρ. For example, such dependence ρ(t) is observed for the Cu 3 Al ordered compound (L1 2 ) [7]. On the contrary, an abrupt drop in resistivity is characteristic of the Ni 3 Al alloy upon decreasing S (coefficient dρ/dt) is negative. This phe nomenon is observed not only for the Ni 3 Al ordered compound but also for some other intermetallic alloys and is associated with the features of their electronic spectrum [8].The temperature of disordering onset (t a ) for the Ni 3 Al alloy is that after which resistivity starts to decrease. If the alloy structure consists of the interme tallic compound (γ'...

Effect of Carbon on the Electrical Resistivity of Ni–Al Intermetallic Alloy Synthesized by an Electrothermal Explosion under Pressure

“…The electrical resistivity ρ of all studied alloys of the Ni-Al-Fe system monotonically increases with increasing temperature, then decreases, and then increases again. A similar behavior of the dependence ρ(t) for Ni 3 Al-based intermetallic alloys was obtained in [13].…”

“…Iron-doped Ni 3 Al ternary alloys have been studied by measuring the electrical resistivity and by differential thermal analysis [13]. It has been shown that the dissolution of Ni 3 Al (γ' phase) is accompanied by a drop in electrical resistivity.…”

EFFECT OF HEAT TREATMENT CONDITIONS ON ELECTRICAL RESISTIVITY OF 35KhGF MOLTEN STEEL

“…Температурный коэффициент удельного сопротивления в режиме охлаждения меньше по абсолютной величине в 4 - 5 раз и отрицателен. Ранее аналогичный результат был получен при измерении удельного электросопротивления жидких жаропрочных сплавов [37]. При охлаждении жидкой стали в этом случае число электронов проводимости z, следовательно, и волновое число Ферми k F увеличивается В соответствие с теорией Фабера-Займана, в данном случае определяющим фактором является рост величины структурного фактора a(2k F ).…”