Maurice M. Karnowsky

Thermal Expansion and Elastic Properties of High Gold-Tin Alloys

The Au-Sn eutectic alloy, composed of the ζ and δ phases, has been used for many years in the sealing of hermetic parts. Recently, it was shown that the ζ phase undergoes an ordering transformation to ζ′. Since this transformation may affect hermeticity, measurements of density, linear thermal expansion coefficient, elastic moduli, and Poisson’s ratio were made on ζ-phase, eutectic, and δ-phase specimens. Measurements were made over a temperature range that includes the ζ → ζ′ transformation. Abrupt changes in these thermophysical properties, near the phase transformation temperature, are noted for ζ and eutectic specimens but not for the δ specimen.

Characterization of crystallization in Metglas 2826 MB alloy

The crystallization behaviour of the Metglas 2826 MB alloy (Fe40Ni38Mo4B18) has been studied using resistance measurements and X-ray diffraction techniques. Three annealing sequences were used to follow the process. Samples were annealed isothermally (a) at 780° C in a vacuum of 2×10−5 torr for times in the range 1 sec to 4 h, (b) for 2 h in an argon atmosphere at temperatures where the resistance curve indicated phase changes to occur, and (c) for 300 h in 100 torr of helium at 400, 600, 700 and 850° C. From these annealing sequences it was found that the alloy did not crystallize below 410° C and followed a crystallization process of: amorphous Fe40Ni38Mo4B18 → FexNi23−xB6 (cubic)+glassy matrix → FexNi23−xB6+(Fe, Ni) (FCC) → (Fe, Ni)3B(bct). This series of transformations was followed for Sequences (a) and (c) above, but was slightly different for Sequence (b). An orthorhombic (Fe, Ni)3 B phase was found in the samples annealed in a vacuum of 2×10−5 torr.

Layer growth in Au-Pb/In solder joints

The solid state reaction between a Pb-In solder alloy and thin film Au has been investigated at ten aging temperatures ranging from 70 to 170°C. Also, bulk Au-solder samples were aged at 150°C for metallographic analysis. No significant difference was found between the aging behavior of thin and bulk Au specimens. A thin single phase layer of Au9In4 was found adjacent to Au while a thick two-phase layer of AuIn2 and Pb was found between Au9In4 and solder. The Pb phase was shown to have considerable mobility and able to ripen at room temperature. Peculiar planar interface instabilities and voids in the Au-Au9In4 interface were found. Although the total layer thicknessvs aging time data could be closely fitted with a power law relationship, it was shown that a linear relationship also fits well and is consistent with accepted metallurgical concepts. An activation energy of 0.61 eV was found by regression analysis of the intermetallic growth kinetics.

Annealing behaviour of amorphous Fe80B20 on continuous heating

Resistance measurements during direct heating of Fe80B20 amorphous alloys indicate phase changes occur at 395, 500, 720 and 840° C. Samples heated to these temperatures, and maintained for five minutes in a neutral atmosphere, show that a hardness maximum occurs at the crystallization temperature of 395° C and that annealing at 500° C produces a material with the same hardness. Above 500° C the microhardness is seen to drop below that of the amorphous alloy. Saturation magnetization measurements show a steady increase following each anneal, up to a temperature of 720° C, and the rate of increase is seen to drop in the range of 720 to 840° C. X-ray diffraction studies show that only a small fraction of the matrix is crystallized following the anneal at 395° C and the transformed phases are α-Fe and Fe3B. Following annealing at 500° C, an increased proportion of α-Fe and Fe3B are observed with complete crystallinity while samples heattreated at 720° C are seen to consist of a three-phase mixture of α-Fe, Fe23B6 and Fe2B. Annealing at 840° C is seen to produce an equilibrium phase mixture of α-Fe and Fe2B phases. Only in the sample annealed at 395° C is a fraction of the amorphous phase seen to persist, indicating that a 5 min anneal is not sufficient, at this temperature, to induce complete crystallization. These structural features are corroborated by field ion microscope analyses, made at liquid nitrogen temperature in a medium of pure neon, and scanning electron microscopy, and are also consistent with our earlier study involving the isothermal annealing, for various times, of Fe80B20 alloy at 780° C.

Effect of composition and high energy rate forging on the onset of precipitation in an iron-base superalloy

The precipitation sequence in a modified A-286 Fe-base superalloy (nominally Fe + 30 pct Ni + 15 pct Cr + 2.0 pct Ti + 1.25 pct Mo + 0.2 pct Al) was examined by optical and electron microscopy and electrical resistance measurements. Secondary phases which precipitate during aging were found to be γ′ in the matrix; (Ti, Mo)C and a boride, M3B2, at grain boundaries; and 17 in three morphologies,i.e., cellular, Widmanstätten, and platelets inside γ′ particles. The exact aging sequence depends upon time, temperature, and pre-age condition. Composite time-temperature-precipitation (TTP) diagrams were developed which show the precipitation sequence for two pre-age conditions,viz., solution treated and high energy rate forged (HERFed). It was found that HERFing prior to aging accelerates γ′ and (Ti, Mo)C precipitation, whereas it has negligible effect on cellular 17 and M3B2 precipitation. HERFing also promotes the precipitation of Widmanstätten 17 and 17 platelets inside γ′ particles.

The Au-In-Pb system:The AuIn2-In-Pb portion

The Au-In-Pb system was investigated in the AuIn-In-Pb portion of the system. Pb-AuIn and Pb-AuIn2 quasibinary systems were found:the first, consisting of a eutectic and a monotectic reaction and the second, a eutectic with an inflection in the liquidus. The chief source of information was differential thermal analyses and verification by metallography, X-ray diffraction and microprobe analyses. Four isothermal reactions were found as follows: 1) L1 ⇌ L2 + AuIn2 + AuIn at 433°Celsius 2) L1 ⇌ Pb + AuIn2 + AuIn at 316°Celsius 3) Pb + L ⇌ α + AuIn2 at 172°Celsius 4) α1 + L ⇌ AuIn2 + In at 159°Celsius. Verification of these events and the isopleth from 50-50 wt pct Pb-In, a typical solder, to ≈ 47 wt pct Au are given.

The phase diagram for the binary system K2CrO4CaCrO4

Abstract The phase diagram for the binary system K 2 CrO 4 CaCrO 4 has been determined for CaCrO 4 concentrations up to 60 mole%, using the techniques of differential thermal analysis, X-ray diffraction, and drop calorimetry. Essential features of the phase diagram are: the solid-solid phase transition for pure K 2 CrO 4 at 670°C, β-K 2 CrO 4 ⇄ α-K 2 CrO 4 ; a eutectoid reaction at 14 mole% CaCrO 4 and 548°C, β-K 2 CrO 4 ⇄ α-K 2 CrO 4 + K 2 CrO 4 · CaCrO 4 ; a peritectoid event at 50 mole% CaCrO 4 and 640°C, β-K 2 CrO 4 + CaCrO 4 ⇄ K 2 CrO 4 · CaCrO 4 ; and a eutectic reaction at 51 mole% CaCrO 4 and 678°C, L ⇄ β-K 2 CrO 4 + CaCrO 4 . X-ray diffraction studies lead to the determination of the unit cell dimensions for the K 2 CrO 4 · CaCrO 4 double salt, a C -centered monoclinic form with a 0 = 7.615(6) A, b 0 = 22.797(15) A, c 0 = 9.777(9) A, β = 115.45(5)°.

The phase diagram of the system Li2CrO4K2CrO4

Abstract The Li 2 CrO 4 K 2 CrO 4 phase diagram was determined by using differential thermal analyses with confirmation by high-temperature X-ray diffraction. The outstanding features are the formation of a eutectic composition of ∼22.5 mole% K 2 CrO 4 between Li 2 CrO 4 and the double salt, δ-Li 2 CrO 4 · K 2 CrO 4 , at 390°C; the formation of a congruently melting double salt Li 2 CrO 4 · K 2 CrO 4 with three solid state allotropic forms, γ, δ, and e, the d spacings and colors of which are given; and the formation of a eutectic composition at ∼54 mole% K 2 CrO 4 between αK 2 CrO 4 and the double salt, γ-Li 2 CrO 4 · K 2 CrO 4 , at 525°C.