Precipitation Of Intermetallic Phases Research Articles

Structure and properties of intermetallic phases in stainless alloy 06KhN28MDTL for shaped castings

1. Nonfulfillment of the specified heat treatment may lead to formation of excess phases in the form of large light inclusions, films in the grain boundaries, and colonies of fine needles in castings of alloy 06KhN28MDTL after quenching. Microprobe analysis showed that all of them have the same composition: 37.0–39.0% Cr, 9.0–10.5% Mo, 1.6–2.0% Si, 14.0–16.0% Ni, and 31.0–33.0% Fe (carbon determined qualitatively), with high (in comparison with austenite) concentrations of Mo, Cr, Si, and C and low concentrations of Ni and Fe. 2. Brittle intermetallic phases in castings of alloy 06KhN28MDTL are thermally stable and do not go into solution at temperatures up to 1200°, which excludes the possibility of correcting the structure of shaped castings by repeated heat treatment. 3. To prevent precipitation of intermetallic phases in shaped castings, we recommend that the chemical composition of alloy 06KhN28MDTL be corrected — reduction of the molybdenum content to 2.4–2.8%, chromium to 21.0–23.0%, and limiting the silicon content to 0.6% and the amount of residual aluminum to 0.08%.

Recrystallization and aging effects associated with the high temperature deformation of waspaloy and inconel 718

Cylindrical samples of Waspaloy and Inconel 718 were hot compressed, using a computerized Instron machine. The test program covered strain rates from 10•4 s•1 to 1 s•1 temperatures ranging from 875 °C to 1220 °C and deformations up to strains of 0.7. Interrupted tests were also carried out to determine the nature of the static softening and hardening processes. Dynamic recrystallization, partial or complete, was observed at temperatures above 950 °C. At 950 °C and below, dynamic recovery was the process controlling the deformation. Static softening was found to take place both by recovery and by recrystallization. Yield points were detected in Waspaloy under certain conditions as well as in Inconel 718. For Waspaloy the yield drops occurred in the vicinity of 1100 °C, and a deviation from the normal behavior in the stress-temperature curve was seen in the same temperature range. The mechanism responsible for the occurrence of the yield drops, which in turn is related to the deviation in the σvsT curve, is believed to be short range ordering of the γ’ forming elements. For Inconel 718, elements such as Co, Cr and Fe may be causing short range ordering, but the locking mechanism may also be associated with the precipitation of carbides or other intermetallic phases on the dislocations.

Thermal Stability of Metastable Phases Produced by Laser Treatment of Aluminium Implanted With Chromium and Molybdenum

ABSTRACTWe present a first He ion channeling study on thermal stability (under isochronal vacuum furnace annealing at 300-650°C) of metastable solid solution phases produced by pulsed ruby laser treatment of Al implanted with Cr and Mo. Laser treated Cr exhibits strong redistribution inferred to be due to intermetallic phase precipitation which appears to be enhanced by quenched-in defects. In contrast, laser treated Mo shows no redistribution but only a loss of substitutionality. Instead of annealing, thermal treatment produces an increase in host dechanneling yield for all laser treated samples. Detailed comparison with thermal recovery of as implanted phases demonstrates the key role played by quenched-in defects.

Phase instability and corrosion behaviour of AISI 316 P/M stainless steel

AbstractThe corrosion behavior of metal powder compacts of different densities made from AISI 316 stainless steel prealloyed powder, heat‐treated at different temperatures and times was investigated. Microcharacterisation of polished and fracture surfaces was performed by scanning electron microscopy. Energy dispersive X‐ray analysis was used to identify precipitated phases. The anodic and cathodic polarization curves in 1 N sulfuric acid were compared with those of a wrought alloy of similar composition. A distinct difference in the electrochemical behaviour of the powdermetallurgical and the wrought alloy was found. This was attributed to enhanced precipitation of intermetallic phases in the P/M‐alloy due to grain‐size and density factors.

Creep and rupture in Type 316 stainless steel at temperatures between 525 and 900°C Part III: Precipitation behaviour

The precipitation in the heavily deformed gauge portions and the undeformed heads of initially solution-treated Type 316 austenitic stainless steel specimens tested in creep-rupture at temperatures in the range 525 to 900°C has been examined using a range of metallographic techniques. M23C6 carbide precipitation occurred very rapidly whereas the intermetallic phases precipitated after much longer times over the range of temperatures investigated. Concurrent creep straining significantly increased the rate of both the carbide and intermetallic phase precipitation. The present results confirm the previous understanding of the precipitation in this steel including the effects of some compositional and thermomechanical variables.

An Improved Ni-Cr-Mo Alloy for Corrosion Service

Abstract A new Ni-Cr-Mo corrosion resistant alloy, Hastelloy alloy C-4, has been developed that does not precipitate an intermetallic Mu phase upon aging in the 650 to 1090 C temperature range. This further improvement of Hastelloy alloy C-276 has evolved from a detailed study of the effects of the substitutional and interstitial elements on the precipitation of intermetallic and carbide phases. Data have been generated to show that Hastelloy alloy C-4 is basically equivalent in corrosion resistance to its predecessors in both oxidizing and reducing media.

New Ni‐Cr‐Mo alloy demonstrates high‐temperature structural stability with resultant increases in corrosion‐resistance and mechanical properties

AbstractEquipment made of NiCrMo alloys of the Ni 16 Cr 16 Mo W and Ni 22 Cr 16 Mo types is used extensively in the chemical industry, in particular because the corrosion resistance in the as‐welded condition could be improved in recent years by controlling C and Si contents to very low levels. A new type of alloy — Hastelloy Developmental Alloy C‐455 — has high resistance to carbide and intermetallic phase precipitation at high temperatures. By reducing the amount of these phases it has been possible to considerably improve the high temperature properties, the corrosion resistance and the mechanical properties of the alloy. The new material may be exposed to sensitizing range temperatures (550–1090 °C) for a long time without becoming susceptible to corrosion: it is, therefore, readily weldable. Contrary to NiCrMo alloys known so far there are almost no problems when the material is exposed to hydrochloric and sulfuric acids.

Intercrystalline corrosion of high-silicon stainless steel

1. Susceptibility to ICC depends to a considerable extent on the character of the corrosive medium, other conditions being equal. 2. Steel 000Kh20N20S5 is not susceptible to ICC after AM and D tests (GOST 6032-58), but is susceptible to ICC in a more highly oxidizing medium. 3. Brittleness and susceptibility to ICC are induced by precipitation of intermetallic phase. 4. Steel 000Kh20N20S5 is recommended for welded structures if it is heat treated after welding.

Mechanical properties of steel Kh15N5D2T after heat treatment

1. Annealing of hot-rolled steel Kh15N5D2T at 580–700°C leads to the α→γ transformation, accompanied by higher plasticity. 2. After normalization and low-temperature aging the steel is strengthened as the result of the martensitic transformation and the precipitation of excess intermetallic phase.

Phase transformations in tool alloys with intermetallic-carbide hardening

1. The iron-base tool alloy (0.3–0.4% C, 20% W, 20% Co, 4% Cr), which is hardened by precipitation of intermetallic and carbide phases, consists of Feα phase, M6C carbide, and the intermetallic compound Co7W6 in the annealed condition. 2. The extent of decarburizing can be determined from the relative intensities of the Co7W6 and M6C lines on the x-ray patterns. 3. During heating to quenching temperature the Co7W6 is dissolved first, and then M6C. All the Co7W6 is dissolved at 1150°C, while part of the M6C remains in the form of excess carbide even after quenching from 1350°C. 4. The Ms-Mf points of the alloy are 130–150°C higher than for high-speed steels of the usual composition and the Mf point is above room temperature, due to which the quenched alloy contains practically no residual austenite. 5. The hardness of the alloy as cast, annealed, and quenched is approximately the same (HRC 40-45). 6. The absence of residual austenite after quenching permits single tempering of the alloy. 7. The alloy is hardened in tempering at 560–630°C due to the precipitation of carbide and inter-metallic phases. The hardness is increased to HRC 67 at a red hardness of Kr58 up to 720°C and strength σbend up to 240 kg/mm2, and the cutting and technological properties are high.

Effect of silicon on temper brittleness of chromium-nickel steel of the Kh20N20 type

1. Steel Kh20N20 alloyed with up to 5% Si is not embrittled on tempering up to 10 h. With 6% Si the steel is embrittled in 1 h. 2. The embrittlement of steel Kh20N20 with 6% Si and steel Kh20N20 with more than 4% Si on prolonged tempering (over 100 h) is evidently due to the precipitation of an intermetallic phase enriched in silicon.

Sintering of mixtures of powders of nickel and molybdenum

1. Mixtures of powders of carbonyl nickel and molybdenum for preparing cermet alloys are easily pressed and sintered and do not require any special measures for protection from oxidation during sintering (careful drying of hydrogen and use of covers). 2. Cermet nickel molybdenum alloys obtained from mixtures of dispersed powders are practically homogeneous after sintering for 1–2 h at 1473°K. The processes of homogenization take place more actively in alloys obtained from mixtures of powders than in cast alloys. 3. With increase in molybdenum content in the alloy, beginning from 25%, there is observed a decrease in the rate of increase in electrical resistance which is connected with a denudation of the solid solution with molybdenum because of precipitation of intermetallic phases. 4. The strength of the alloys increases with increase in concentration of molybdenum. The cermet alloy Ni-30 Mo sintered at 1473 °K has a strength of 60 kg/mm2 and an impact strength of 7.5 kgm/cm2. The decrease in strength and impact resistance for alloys of Ni-35% Mo sintered at 1473°K is explained by embrittlement of the material because of precipitation of intermetallic phases along the grain boundaries. 5. After sintering at temperatures of above 1500°K, alloys of Ni-35% Mo have a greater strength than Ni-30% Mo alloys. The decrease in strength of Ni-30% Mo and Ni-35% Mo alloys sintered at 1573°K, compared with alloys sintered at 1523 °K, is explained by embrittlement of the material because of the sharp increase in grain size at 1573°K.