Engineering topics

Thompson, R. G.

Publications and source records attributed to Thompson, R. G..

11 records

NASA NTRS1990

Effect of boron on intergranular hot cracking in Ni-Cr-Fe superalloys containing niobium

Solidification mechanisms had a dominant influence on microfissuring behavior of the test group. Carbon modified the Laves formation significantly and showed that one approach to alloy design would be balancing carbide formers against Laves formers. Boron's strong effect on microfissuring can be traced to its potency as a Laves former. Boron's segregation to grain boundaries plays at best a secondary role in microfissuring.

Thompson, R. G.↗

NASA NTRS1988

Microstructure And Weld Cracking In Inconel 718(R)

Theories on relationship between metallurgy and microfissuring confirmed. Report describes research on effects of microstructure on cracking of heat-affected zones of welds in Inconel 718(R) alloy. In experimental studies, specimens subjected to various combinations of time-varying thermal and mechanical stresses to simulate welding conditions and to identify physical and chemical effects causing microfissuring.

Thompson, R. G.↗

NASA NTRS1986

The effect of heat treatment on microfissuring in alloy 718

Changes in the microfissuring susceptibility of alloy 718 due to solution annealing and age hardening are studied. The effects of Ni3Nb (delta) precipitation during solution annealing and gamma-prime + gamma-double-prime precipitation during age hardening on microfissuring are investigated. It is observed that solution annealing reduces microfissuring and age hardening increases it, and the two precipitates do not affect microfissuring susceptibility. Potential causes for the detected intergranular segregation of the alloy are discussed.

Thompson, R. G.↗

NASA NTRS1985

Relationships between microstructure and microfissuring in alloy 718

Microfissures which occur in the weld heat affected zone of alloy 718 can be a limiting factor in the material's weldability. Several studies have attempted to relate microfissuring susceptibility to processing conditions, microstructure, and/or heat-to-heat chemistry differences. The present investigation studies the relationships between microstructure and microfissuring by isolating a particular microstructural feature and measuring microfissuring as a function of that feature. Results to date include the identification of a microstructure-microfissure sequence, microfissuring susceptibility as a function of grain size, and microfissuring susceptibility as a function of solution annealing time.

Thompson, R. G.↗

NASA NTRS1984

Hot Microfissuring in Nickel Alloy

Experiments in intergranular cracking of nickel alloy near solidus temperature discussed in contractor report. Purpose of investigation development of schedule for welding, casting, forging, or other processing of alloy without causing microfissuring.

Thompson, R. G.↗

NASA NTRS1984

Microfissuring in Nickel-Based-Alloy Welds

Cracking mechanisms proposed. Investigation of physical metallurgy of near-solidus integranular cracking or microfissuring in Inconel 718 alloy welds described in report. Investigation sought to identify cause of microfissuring and quantify its behavior.

Thompson, R. G.↗

NASA NTRS1983

Microstructural evolution in the HAZ of Inconel 718 and correlation with the hot ductility test

The nickel-base alloy 718 was evaluated to study the role of preweld heat treatment in reducing or eliminating heat-affected zone hot cracking. Three heat treatments were studied using the Gleeble hot ductility test. A modified hot ductility test was also used to follow the evolution of microstructure during simulated welding thermal cycles. The microstructural evolution was correlated with the hot ductility data in order to evaluate the mechanism of hot cracking in alloy 718. The correlation of hot ductility with microstructure showed that recrystallization, grain growth, and dissolution of precipitates did not in themselves cause any loss of ductility during cooling. Ductility loss during cooling was not initiated until the constitutional liquation of NbC particles was observed in the microstructure. Laves-type phases were found precipitated in the solidified grain boundaries but were not found to correlate with any ductility loss parameter. Mechanisms are reviewed which help to explain how heat treatment controls the hot crack susceptibility of alloy 718 as measured in the hot ductility test.

Thompson, R. G.↗

NASA NTRS1982

On relationship between microfissuring and microstructure in the HAZ of Inconel 718

Inconel 718, as well as many other metals, is susceptible to intergranular hot cracking in the weld heat-affected-zone (HAZ). These cracks form near the solidus temperature of the metal during the welding process. This problem is of particular concern to NASA/MSFC because the SSME is primarily constructed of welded Inconel 718. The present program studied microfissuring in the weld HAZ of Inconel 718 by simulating HAZ thermal cycles with the Gleeble machine. Previous researchers have studied the instantaneous mechanical properties of the HAZ using the Gleeble. The present study examines the instantaneous microstructure of the HAZ. This approach showed that second phase structures, high in niobium, melt and wet the grain boundaries in the HAZ during welding. It is postulated that the resultant HAZ grain boundaries, enriched in niobium, act as preferred sites for microfissure nucleation as the weld zone cools.

Thompson, R. G.↗

NASA NTRS1981

Further Study of near Solidus Intergranular Cracking in Inconel 718

A series of tests, performed to determine the strain necessary to initiate intergranular cracking in Inconel 718 as a function of temperature, contained enough scatter near the melting temperature that questions remained as to the best curve of curves to fit to the data. Fracture surface analysis showed that the scatter was due to incipient melting in the grain boundary region. The melting contributed to low fracture strain but had only a small on the incipient cracking strain. Gleeble tests, which could be interrupted by water quenching, were used to study the incipient intergranular melting of Inconel 718. This modified weld simulation test provided a sufficiently rapid quench to preserve the intergranular microstructure created during incipient melting. This structure was studied both microscopically and with energy dispensive X-ray analysis. The implications of incipient melting and low-strain incipient cracking on the development of microfissuring envelopes are discussed.

Thompson, R. G.↗

NASA NTRS1974

National economic models of industrial water use and waste treatment

The effects of air emission and solid waste restrictions on production costs and resource use by industry is investigated. A linear program is developed to analyze how resource use, production cost, and waste discharges in different types of production may be affected by resource limiting policies of the government. The method is applied to modeling ethylene and ammonia plants at the design stage. Results show that the effects of increasingly restrictive wastewater effluent standards on increased energy use were small in both plants. Plant models were developed for other industries and the program estimated effects of wastewater discharge policies on production costs of industry.

Thompson, R. G.↗

NASA NTRS1974

Economic modeling and energy policy planning

A structural economic model is presented for estimating the demand functions for natural gas and crude oil in industry and in steam electric power generation. Extensions of the model to other commodities are indicated.

Thompson, R. G.↗