[Paper Review] NiTi Single Crystal Growth by Micro-Pulling-Down Method: Experimental Setup and Material Characterization

Timon Sieweke, Chris Luther+15 more|arXiv (Cornell University)|Jan 9, 2026

Shape Memory Alloy Transformations0 citations

TL;DR

The paper presents a vacuum-based micro-pulling-down apparatus to grow NiTi single crystals and characterizes as-grown crystals using EBSD, SEM, EDX, XPS, hot gas extraction, and DSC, highlighting dopant sensitivity and the advantage of the μPD method for introducing dopants.

ABSTRACT

Nickel-titanium that has an austenite to martensite phase transition has been studied extensively in the past as a shape memory alloy, but a lot remains to be learned from such phase transitions. However, single crystals are needed for a detailed characterization of the emerging phase transition. In order to produce NiTi single crystals for research purposes, we have set up a micro-pulling-down ($μ$PD) apparatus. The $μ$PD process is a fast and flexible method for the fabrication of small single crystals. The apparatus is operated in vacuum. By pulling the crystal down through a hole in the crucible bottom, it is possible to reduce oxygen contamination, since oxides float on top of the melt due to their low density. Here we present a detailed characterization of as-grown NiTi crystals by electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), hot gas extraction method and differential scanning calorimetry (DSC). The characteristics of the phase transition in NiTi are very sensitive to dopants and alloying. The $μ$PD method facilitates the introduction of different doping elements into the crystal.

Motivation & Objective

• Motivate the need for NiTi single crystals to study the austenite-martensite phase transition.
• Describe the micro-pulling-down (μPD) apparatus and its operation in vacuum to reduce oxygen contamination.
• Demonstrate how the μPD process enables controlled dopant incorporation into NiTi crystals.
• Provide a detailed characterization workflow for as-grown NiTi crystals (EBSD, SEM, EDX, XPS, hot gas extraction, DSC).

Proposed method

• Describe the μPD apparatus and its vacuum operation.
• Explain pulling the crystal down through a hole in the crucible bottom to reduce oxides.
• Apply EBSD, SEM, EDX, XPS, hot gas extraction, and DSC for material characterization.
• Highlight the role of dopants and alloying on NiTi phase transition behavior.
• Outline the potential for introducing different dopants via μPD during growth.

Experimental results

Research questions

• RQ1 How does the μPD setup influence oxygen contamination in NiTi single crystals?
• RQ2 What are the microstructural and chemical characteristics of NiTi single crystals grown by μPD as revealed by EBSD, SEM/EDX, XPS, and DSC?
• RQ3 How does the μPD method facilitate dopant incorporation and what is its effect on the phase transition of NiTi?
• RQ4 What is the relationship between the as-grown crystal characteristics and the observed phase transition properties?
• RQ5 Can the μPD approach be used to systematically study dopant effects on NiTi crystals?

Key findings

• The μPD apparatus enables vacuum growth and reduced oxygen contamination by allowing oxides to float on the melt.
• As-grown NiTi crystals were characterized by EBSD, SEM, EDX, XPS, hot gas extraction, and DSC.
• Phase-transition behavior in NiTi is highly sensitive to dopants and alloying elements.
• The μPD method supports introducing different dopants into the crystal during growth.
• The study provides a detailed experimental setup and characterization workflow for NiTi single crystals.