Showing papers on "Alloy published in 1977"

Hardness of tempered martensite in carbon and low-alloy steels

Abstract: This paper presents the results of a systematic study of the effect of carbon, manganese, phosphorus, silicon, nickel, chromium, molybdenum, and vanadium on the hardness of martensite in low to medium carbon steels tempered for one hour at 100°F (56°C) intervals in the range 400 to 1300°F (204 to 704°C). Results show that the as-quenched hardness depends solely on carbon content. On tempering, the effect of carbon on hardness decreases markedly with increasing tempering temperature. Studies of carbon-0.5 manganese steels showed that the incremental increase in hardness from 0.5 pct manganese after a given tempering treatment was independent of carbon content. Based on this result, studies of the effects of the other alloying elements were made using a 0.2 or 0.3 pct carbon, 0.3 to 0.5 pct manganese steel base composition. The hardness of the resulting tempered martensite was assumed to be due to a given alloy addition, and when two or more alloying elements were added, their effects were assumed to be additive. Each of the seven alloying elements increased the hardness of tempered martensite by varying amounts, the increase being greater as more of each element was present. Nickel and phosphorus have substantially the same effect at all tempering temperatures. Manganese has essentially the same hardening effect at any temperature in the range 700 (371°C) to 1300°F; silicon is most effective at 600°F (316°C), chromium at 800°F (427°C), molybdenum at 1000 to 1100°F (538 to 592°C), and vanadium at 1200°F (649°C). Using the data obtained, a procedure is established for calculating the hardness of tempered martensite for carbon and alloy steel compositions in the range studied and for any combination of tempering time and temperature.

Ordering transformations and mechanical properties of Ti 3 Ai and Ti 3 Al-Nb alloys

Abstract: Phase transformations and the kinetics of domain growth were studied in near stoichiometric Ti3Al and in a similar alloy containing about 5 at. pct Nb (Cb). The alloys were quenched from the β and from the α+ β fields and were subsequently annealed in the α2 field to study the ordering transformation. The critical temperature (T c) for ordering was found to be between 1125 and 1150° for both alloys. When quenched from aboveT c the microstructure of the stoichiometric compound contained massive martensite with small antiphase domains of average size 8 × 10— μm. On annealing the quenched structures in the range 700 to 1000°, domain coalescence occurred, the domains growing approximately as the square root of the annealing time. The activation energy for the domain growth process was found to be 64.6 ± 6 Kcal/mole (2.68 ± 0.25 × 105 J/mole). On quenching the alloy containing Nb the β transforms to a fine acicular martensite. On annealing, antiphase domain coalescence within the martensite plates and the simultaneous recrystallization of the martensite resulted in a fine subgrain structure even after annealing at 900° for up to 3 h. The mechanical properties and the fracture modes of the two alloys tested at 700° were correlated with the observed microstructural changes. The effects of Nb in this alloy are to slow the domain growth kinetics, to reduce the planarity of slip, and to increase nonbasal slip activity.

Calorimetric studies of 7000 series aluminum alloys: I. Matrix precipitate characterization of 7075

Abstract: Both differential scanning calorimetry (DSC) and hot stage transmission electron microscopy were used to characterize the solid state reactions accompanying heating of the highest strength (T651) and overaged (T7351) tempers of 7075 aluminum alloy. Each of the observed endothermic or exothermic reactions that occurs over the 20 to 500°C temperature range has been ascribed to the dissolution or formation of a specific precipitate. The dissolution of each matrix phase,i.e., GP zones, ή and ή, can be characterized by a distinguishable dissolution temperature, dissolution enthalpy, activation energy, and activation entropy. The values of activation energy and activation entropy for the dissolution of the initial matrix precipitate of these phases indicate that the relative stability of the matrix precipitates is primarily influenced by the entropy rather than the energy term. This investigation provides a basis for the use of DSC analysis in the rapid, quantitative identification of the matrix microstructure of 7075 aluminum alloy as well as in the characterization of the matrix microstructure of other 7000 series aluminum alloys.

Oxidation of aluminum-magnesium melts in air, oxygen, flue gas, and carbon dioxide

Abstract: Oxidation rates of aluminum—1 to 14 pct magnesium melts in air, oxygen, flue gas, and carbon dioxide at temperatures from 600 to 1100°C were measured with an automatic recording balance. For most conditions, a protective amorphous film on the melt surface kept the oxidation rate low initially. After an interval that was shortened by increasing temperature or magnesium content, the film crystallized to magnesium oxide and magnesium aluminate, accompanied by a sudden increase in oxidation rate. Known as breakaway oxidation, this phenomenon could be produced by adding crystalline magnesium oxide or magnesium aluminate seed to melts protected with amorphous oxide. Flue gas or carbon dioxide in the atmosphere, sodium or beryllium in the alloy, or boron dusted on the surface delayed crystallization unless seed was added. Beryllium was the most effective. Flue gas from burning natural gas delayed breakaway oxidation of unseeded melts containing up to about 4 pct magnesium at normal melting furnace temperatures near 750°C. Slow melting of solid aluminum-magnesium alloy concentrated magnesium in the first liquid to melt, sharply decreasing the interval before breakaway oxidation after melting. Rapidly melting the solid increased the protective interval. Homogenizing the solid just below the melting range before rapid melting further extended the interval before the onset of breakaway oxidation.

Deposition method and products

Abstract: A method of depositing a hard metal alloy is described wherein a volatile halide of titanium is reduced off the surface of a substrate and then reacted with a volatile halide of boron, carbon or silicon to effect the deposition on a substrate of an intermediate compound of titanium in a liquid phase. The liquid compound on the substrate is then reacted in the presence of hydrogen to produce a hard deposit containing titanium and boron, carbon or silicon. Also described are products which may be produced by the above method.

Kinetics of thin-film reactions between Pb and the AgPd alloy

Abstract: Thin‐film reaction between Pb and the Ag‐20 at.% Pd alloy in the temperature range 160–200 °C has been studied by x‐ray diffraction. The reaction results in the formation of the Pb2Pd compound by depleting Pd from the alloy. The rate of depletion is too fast to be explained by lattice diffusion in the alloy at these temperatures. In fact, it is shown that the intermixing of Ag and Pd to form the alloy by lattice diffusion can only occur around 450 °C. On the other hand, grain‐boundary diffusion is faster, but it is not obvious how Pd atoms within the alloy grains can be depleted by grain‐boundary diffusion. To overcome this difficulty, a kinetic model with a moving interface has been developed to explain the low‐temperature reaction. The model seems to agree quite well with the experimental results.

High strength low alloy structural steels

Abstract: The development of high strength low alloy structural steel has been a remarkable achievement in the field of metallurgy and is of great interest to both the producers and users of structural steels. Higher strength of the steel permits lighter constructions to be made with thinner sections giving rise to steel economy, increase of payload of transport vehicles and a greater utilisation of the design advantages. Of the various techniques available to enhance the properties of structural steels, addition of grain refining and precipitation hardening elements, niobium, vanadium and titanium, to low carbon steels and their controlled rolling or normalising have been found most advantageous. The alloying element required for making these steels is in micro-quantities and a large part of the strength is derived through grain refinement, which also contributes towards toughness. Various factors that control the properties of structural steels such as the effect on strength of the element in solid solution, ferrite grain size, strengthening by precipitation in ferrite, dislocation strengthening and pearlite volume and its fineness, have been discussed. Results of laboratory scale experiments carried out in NML have been summarised. Results of industrial scale trails on the production and controlled rolling of niobium steels carried out in Rourkela Steel Plant have been discussed. (Dr. S.S. Bhatnagar, Shri B.K. Guha, Shri R.K. Sinha; Scientists, National Metallurgical Laboratory. Dr. N.S. Datar, General Superindentent, Rourkela Steel Plant. Dr. R. Chattopadhyay, former Scientist, National Metallurgical Laboratory)

Diffusion of titanium in copper

Abstract: Interdiffusion coefficients in copper-titanium alloys have been determined by Matano's method in the temperature range between 973 and 1283 K on (pure Cu)-(Cu-1.98 at. pct Ti alloy) and (pure Cu)-(Cu-2.91 at. pct Ti alloy) couples. Temperature dependence of the impurity diffusion coefficient of titanium in copper, determined by extrapolation of the concentration dependence of the interdiffusion coefficient to zero mole fraction of titanium, is expressed by the following Arrhenius equation along with the probable errors:D Ti/Cu=(0.693 −0.135 +0.169 )×10−4exp[−(196±2)kJ mol−1/RT] m2/s. The difference in the activation energies for the impurity diffusion of the 3d-transition metals and self-diffusion in copper has been calculated by applying LeClaire's model with the oscillating potential of the impurity atom in copper. The calculated values agree well with the experimental values including the present one.

Low-temperature thermal conductivity of an amorphous palladium silicon alloy

Abstract: The thermal conductivity of a glassy PdSi alloy has been measured in the temperature range 0.1–30 K. The thermal conductivity contributed by the phonons has the same anomalous behavior as found for all non-metallic amorphous materials. Heat treatment increases the phonon thermal conductance by ∼50%, a change which does not appear to be related to partial crystallization.

Auger study of preferred sputtering on Ag–Au alloy surfaces

Abstract: Auger electron spectroscopy has been used to investigate the preferred sputtering behavior on homogeneous Ag‐Au alloy surfaces. Measurements were made on a range of alloy compositions with Ar+ sputter ions of 0.5–2 keV energy. The time variation of the surface composition during sputtering was analyzed according to a kinetic model which specifically accounts for the composition change caused by sputtering in the altered layer. Based on this analysis, we were able to determine the individual sputter yields for Ag and Au atoms in the alloy and the depth of the altered layer. The sputter yields were found to increase almost linearly with energy but remained almost constant with the alloy composition. The depth of the altered layer was found to be about 15–30 A.

Deformation-Mechanism Maps for Pure Iron, Two Austenitic Stainless Steels, and a Low-Alloy Ferritic Steel

Abstract: The construction of deformation-mechanism maps for ferrous alloys is described. Maps for pure iron, 316 and 304 stainless steel, and a ferritic 1 percent Cr-Mo-V steel are presented, and their use is illustrated. The maps are constructed, as far as possible, from model-based constitutive laws which have been fitted to experimental data. They attempt to combine the understanding of the fundamentals of dislocation mechanics and diffusion theory with the observation of the yielding and creep of commercial steels. In this way we retain some of the predictive power that an understanding of fundamentals permits, while giving a good description of the observed behavior of the alloys.

Method of imparting a fine grain structure to aluminum alloys having precipitating constituents

Abstract: A method is provided for imparting a fine grain structure to aluminum alloys which have precipitating constituents. The alloy is first heated to a solid solution temperature to dissolve the precipitating constituents in the alloy. The alloy is then cooled, preferably by water quenching, to below the solution temperature and then overaged to form precipitates by heating it above the precipitation hardening temperature for the alloy but below its solution treating temperature. Strain energy is introduced into the alloy by plastically deforming it at or below the overaging temperature used. The alloy is then subsequently held at a recrystallization temperature so that the new grains are nucleated by the overaged precipitates and the development of these grains results in a fine grain structure.

Electronic theory for segregation at the surface of transition-metal alloys

Abstract: A tight-binding-type electronic theory for the atomic segregation at the surface of transition-metal alloys is presented Results are given showing the dependence of the segregation on the electronic alloy parameters

Method for improving fatigue properties of titanium alloy articles

Abstract: A thermomechanical treatment to improve the fatigue strength of articles made from one of a class of alpha beta titanium alloys. The treatment involves heating the alloy into the beta field, hot deforming the alloy at a temperature within the beta field, rapidly quenching the alloy to room temperature to produce a hexagonal martensite structure and then tempering at an intermediate temperature so as to produce a structure in which discrete equiaxed beta phase particles are presented in an acicular alpha matrix. This structure is particularly resistant to the initiation and propagation of fatigue cracks.

Permanent magnet alloy

Abstract: PURPOSE: To increase the Curie point and coercive force (Hc) of a permanent magnet and to improve the thermal stability by substituting Si for part of B in the magnet made of an intermetallic compound consisting of a rare earth metal, Fe, Co and B. CONSTITUTION: An alloy having a composition represented by formula 1 (where R is one or more kinds of rare earth elements, 0≤x≤0.5, 0.02≤y≤0.3, 0.002≤z ≤0.15, and 4≤A≤7.5) is melted in vacuum or a gaseous Ar atmosphere, and the molten alloy is cast into an ingot. This ingot is pulverized in a gaseous N 2 atmosphere, and the resulting powder is press-molded in a magnetic field of 15kOe. The molded body is sintered in a gaseous Ar atmosphere, and the sintered body is rapidly cooled and heat treated at 400W800°C. Thus, an intermetallic compound having a composition contg. Si substituted for part of B is formed, and a permanent magnet made of the compound consisting of rare earth metals, Fe, Co, B and Si is obtd. This permanent magnet has an increased Curie point, increased coercive force (Hc) and superior thermal stability. COPYRIGHT: (C)1985,JPO&Japio