Microstructural development in cast and laser beam clad nickel aluminum bronze

The microstructural development in full and quarter scale nickel aluminum bronze (NAB) propeller castings and laser beam clad (LBCL) NAB were characterized in detail to further the fundamental understanding of the phase transformations and resultant properties that occur in this alloy.; A specimen of such large scale specimen weight was {dollar}>{dollar}30,000 Lbs) has never been available for in depth chemical and structural characterization. The large specimen size and subsequently its coarse constituents have allowed very clear viewing and more precise characterization of phases and phase transformations not previously resolvable.; In the as-received full scale casting, the microstructure primarily consisted of Widmanstatten rods of proeutectoid {dollar}alpha{dollar}, the eutectoid mixture of {dollar}alpha{dollar} + {dollar}kappa{lcub}rm iii{rcub}{dollar}, and {dollar}kappasb{lcub}rm iv{rcub}{dollar} and {dollar}kappasb{lcub}rm ii{rcub}{dollar} precipitates. No martensite was observed. The {dollar}kappasb{lcub}rm i{rcub}{dollar} phase was observed in the NAB quarter scale propeller casting. This phase was found to be stable in the melt. Through DTA analysis, NAB was determined to be 100% liquid at 1062{dollar}spcirc{dollar}C and 100% solid at 1016{dollar}spcirc{dollar}C. In addition, the Al content of the alloy was found to strongly influence the resultant microstructure.; Heat treatment, i.e., isothermal transformation and continuous cooling, studies allowed the determination of the microstructural evolution in the base metal casting and provided a means of developing a better understanding of the phase transformations (e.g., eutectoid reaction) which occur in NAB. Subsequent analyses were performed using light microscopy and EPMA.; Isothermal transformation temperatures from 1000{dollar}spcirc{dollar}C to 500{dollar}spcirc{dollar}C were investigated. A semiquantitative TTT curve for NAB was generated. NAB was found to solidify as 100% {dollar}beta{dollar} phase. However, the 100% {dollar}beta{dollar} phase field was found a be very narrow. The proeutectoid {dollar}alpha{dollar} reaction was impossible to suppress even during rapid quenches from the melt. The proeutectoid {dollar}alpha{dollar} phase was found to form on {dollar}beta{dollar} grain boundaries, as allotriomorphs, at 1000{dollar}spcirc{dollar}C. The morphology of the {dollar}alpha{dollar} phase was found to follow the Dube classification.; NAB was continuously cooled from 1029{dollar}spcirc{dollar}C to 500{dollar}spcirc{dollar}C. Similar to observations during the isothermal transformation study, the first phase to form during continuous cooling of NAB from 1029{dollar}spcirc{dollar}C was proeutectoid {dollar}alpha{dollar} as grain boundary allotriomorphs at 989{dollar}spcirc{dollar}C. By 823{dollar}spcirc{dollar}C, planar interfaces had developed between the {dollar}beta{dollar} and proeutectoid {dollar}alpha{dollar} phases. The proeutectoid {dollar}alpha{dollar} was found to grow via the ledge mechanism. The {dollar}kappasb{lcub}rm ii{rcub}{dollar} and {dollar}kappasb{lcub}rm iv{rcub}{dollar} phases were first observed at 832{dollar}spcirc{dollar}C. The {dollar}kappasb{lcub}rm iii{rcub}{dollar} phase was first observed at 823{dollar}spcirc{dollar}C which marked the start of the eutectoid reaction during continuous cooling. In contrast to what was observed during isothermal transformation, the {dollar}kappasb{lcub}rm iii{rcub}{dollar} phase was present on the {dollar}alpha{dollar} side of the {dollar}alpha{dollar}/{dollar}beta{dollar} interphase interface. At 823{dollar}spcirc{dollar}C, both discrete and lamellar {dollar}kappasb{lcub}rm iii{rcub}{dollar} were observed. A model describing the genesis and evolution of the eutectoid reaction in continuously cooled NAB was presented. EPMA x-ray maps and concentration profiles seem to indicate that a certain level of solute, primarily in terms of N...