B-Ni

Zhang

2013

J. Mater. Res.

Solidification of undercooled Ni-4.5 wt% B alloy melt was investigated by glass fluxing and cyclic superheating. A maximum melt undercooling up to DT p 5 283 K has been achieved. If ΔT p , 175 6 10 K, the primary solidification is L ! Ni 3 B; the structure consists of Ni 3 B dendrite 1 lamellar eutectic; the phase sizes and fractions depend on ΔT p . If ΔT p $ 175 6 10 K, the primary solidification is L ! Ni/Ni 23 B 6 ; the structure consists of the dot-phase region 1 the anomalous eutectic/network boundary; the phase fractions mainly depend on ΔT r ; the dot phases are determined as rod eutectic and dot precipitates, while the network boundary is the divorced eutectic. The solidification pathways show that there is a common critical nucleation temperature, 1227 6 10 K, for metastable eutectic reaction in hypoeutectic and hypereutectic Ni-Ni 3 B alloys.

Section: Solidification Pathwaysmentioning

confidence: 99%

Phase selection of undercooled solidification of Ni–4.5 wt% B alloy

Zhang

2013

J. Mater. Res.

“…1). 5 The eutectic solidification is initiated at Δ T 2 ≈50 K (1366−1316 K), where the Ni–Ni 3 B eutectic forms according to the phase diagram (Fig. 1).…”

Section: Resultsmentioning

confidence: 99%

“…The phase diagram of Ni–Ni 3 B alloy is shown in Fig. 1 5. About 50 years ago, Shapiro and Ford studied orientation and interfacial relations for Ni–Ni 3 B eutectic in the near equilibrium solidification of hypoeutectic and hypereutectic Ni–Ni 3 B alloys (B<5wt-%) 6.…”

Section: Introductionmentioning

confidence: 99%

Undercooled solidification of Ni–3·3 wt-%B alloy and cooling curve description

Materials Science and Technology

Dang

2013

Undercooled solidification of hypoeutectic Ni-3?3 wt-%B alloy has been studied. The microstructure evolution of Ni-3?3 wt-%B alloy indicates that a transition from regular lamellar eutectic to anomalous eutectic exists with increasing undercooling for eutectic transformation. Here, a new model was proposed to describe the cooling curves of undercooled solidification with two-step transformation. Fits of the present model to the cooling curves after different undercoolings show that the predictions of transformed fractions are compatible with the microstructure observation. Furthermore, for hypoeutectic alloy, the size of the primary phase mainly depends on the undercooling for primary solidification, while the fraction of the primary phase mainly depends on the undercooling for eutectic solidification.

“…39 To apply this model, the equilibrium partition coefficients of a-Ni and Ni 3 B phases must be assumed equal; k a-Ni 5 k Ni 3 B 5 0.02 is given according to the Ni-B phase diagram. 35 Other parameters are from Table III. From Fig.…”

Section: Relation Between the Growth Velocity And The Undercoolingsmentioning

confidence: 99%

“…10 The parameters used for the current calculations are shown in Table III. 14,[33][34][35][36][37] The calculation of growth velocity is shown in Fig. 6(a), where the velocity of pure Ni is also shown for comparison.…”

Section: Relation Between the Growth Velocity And The Undercoolingsmentioning

confidence: 99%

In situ observation of solidification of undercooled hypoeutectic Ni–Ni₃B alloy melt

Zhang

2013

J. Mater. Res.

Solidification of undercooled Ni-3.3 wt% B alloy melt was investigated by glass fluxing.If DT e , 140 6 10 K, two recalescences appear, indicating that stable eutectic reaction occurs; if DT e $ 140 6 10 K, three recalescences can be observed, indicating that metastable eutectic reaction occurs. Analysis indicates that the phase fractions of the as-solidified structure can be predicted by the recalescence delay times in the cooling curves. High-speed video images show that the solidification interface of primary solidification changes from single dendritic shape to spherical shape with increasing DT p ; the interface of eutectic solidification changes from many small "dendrites" to a single large one with increasing DT e ; the interface of residual liquid solidification changes from many small rings to a single large one with increasing DT r . The growth velocity of eutectic solidification suggests a coupled growth at small and moderate undercoolings and decoupled growth at large undercooling, whereas that of residual liquid solidification cannot be interpreted by the available models.