<p>Deformation behavior of NiTiCu alloys with Cu levels of 5, 10, and 20 at.% was studied by in-situ synchrotron X-ray diffraction tensile testing. It was found that residual work from cold-forming and stress-relieving processes promotes stress-induced B2 → B19 → B19′ two-step phase transformation in NiTiCu alloys due to its strong effects on material strength and martensite phase stabilities. Regardless of their wide range of Cu-content, all alloys experienced reversible two-step phase transformation during deformation, which produced large recoverable strains upon unloading. The second-phase transformation happened after B19 martensite already experienced severe lattice distortion, which accommodated most of the transformation strain and resulted in a relatively smoother transition to B19′. All alloys displayed similar texture evolution during the two-step transformation: from a strong <InlineEquation ID="IEq262"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40830_2025_533_Article_IEq262.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="93" /> </InlineMediaObject> <EquationSource Format="TEX">${\text{near-}}\{111\}_{\text{B}2}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>near-</mtext> <msub> <mrow> <mo stretchy="false">{</mo> <mn>111</mn> <mo stretchy="false">}</mo> </mrow> <mrow> <mtext>B</mtext> <mn>2</mn> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> fiber to a near-{103}<sub>B19</sub> and finally a strong <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40830_2025_533_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="103" /> </InlineMediaObject> <EquationSource Format="TEX">${\text{near-}}\{ 1\overline{3}0\}_{{{\text{B19}}^{\prime } }}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>near-</mtext> <msub> <mrow> <mo stretchy="false">{</mo> <mn>1</mn> <mover> <mn>3</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> <msup> <mrow> <mtext>B19</mtext> </mrow> <mo>′</mo> </msup> </msub> </mrow> </math></EquationSource> </InlineEquation> textures following their crystal orientation relationship. Despite the negative effect of Cu on B2 → B19 transformation strain, the total transformation strain appears approximately constant across Cu-contents, giving all three alloys the capability of large strain recovery.</p>

Stress-Induced Two-Step Phase Transformation in NiTiCu Alloys

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发表日期：

2025年3月17日

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S. Cai,
J. E. Schaffer,
J. Yan

摘要

Deformation behavior of NiTiCu alloys with Cu levels of 5, 10, and 20 at.% was studied by in-situ synchrotron X-ray diffraction tensile testing. It was found that residual work from cold-forming and stress-relieving processes promotes stress-induced B2 → B19 → B19′ two-step phase transformation in NiTiCu alloys due to its strong effects on material strength and martensite phase stabilities. Regardless of their wide range of Cu-content, all alloys experienced reversible two-step phase transformation during deformation, which produced large recoverable strains upon unloading. The second-phase transformation happened after B19 martensite already experienced severe lattice distortion, which accommodated most of the transformation strain and resulted in a relatively smoother transition to B19′. All alloys displayed similar texture evolution during the two-step transformation: from a strong ${\text{near-}}\{111\}_{\text{B}2}$ $near- {111}_{B 2}$ fiber to a near-{103}_B19 and finally a strong ${\text{near-}}\{ 1\overline{3}0\}_{{{\text{B19}}^{\prime } }}$ $near- {1 \bar{3} 0}_{{B19}^{'}}$ textures following their crystal orientation relationship. Despite the negative effect of Cu on B2 → B19 transformation strain, the total transformation strain appears approximately constant across Cu-contents, giving all three alloys the capability of large strain recovery.