Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles
Xiang Wang  Lin-Jie Zhang  Jie Ning  Sen Li  Liang-Liang Zhang  Jian Long
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China

Received 22 January 2021, Revised 6 April 2021, Accepted 6 May 2021, Available online 2 June 2021.

Abstract

Ti-6Al-4V alloys mad by additive manufacturing (AM) with slower cooling rate (e. g., direct energy deposition (DED)) generally have the problem of severe coarsening of α phase. This study presents a method to refine the microstructure of the primary β phase formed during the solid–liquid transformation, microstructures formed during the β → α + β transformation, and recrystallized microstructures formed during the repeated heating cycles encountered in AM processes. This is accomplished by the in situ precipitation of nano-sized dispersed high-melting-point yttria Y2O3 particles. The addition of micron-sized particles with high melting points can refine primary crystallized grains and transformed grains corresponding to the secondary phase in Ti-6Al-4V alloys. In addition, they can effectively inhibit the recrystallization and growth of prior-deposited metal grains. The microstructural and tensile properties of laser additive manufactured with filler wire Ti-6Al-4V components with different amounts of Y2O3 (0, 0.12, and 0.22 wt%) were investigated. The refining effect of Y2O3 was significant and the tensile strength of Ti-6Al-4V containing 0.22 wt% Y2O3 in the longitudinal and transverse directions was greater than that of Ti-6Al-4V by approximately 12% and 9%, respectively. Concurrently, there was no loss in the elongation of the material in either direction. The strategy of using micron-sized refractory particles to control phase transformation (primary crystallization, solid-state phase transformation, and recrystallization) can be applied to the AM of different metals, in which microstructures are susceptible to coarsening.

Korea Abstract

더 느린 냉각 속도 (예를 들어, 직접 에너지 증착 (DED))를 가진 적층 제조 (AM)에 의해 미친 Ti-6Al-4V 합금은 일반적으로 α상의 심한 조 대화 문제가 있습니다. 이 연구는 고체-액체 변환 중에 형성된 1 차 β상의 미세 구조, β → α + β 변환 중에 형성된 미세 구조, AM 공정에서 발생하는 반복되는 가열주기 동안 형성된 재결정 화 된 미세 구조를 정제하는 방법을 제시합니다.

이는 나노 크기의 분산 된 고 융점이 트리아 Y2O3 입자의 현장 침전에 의해 달성됩니다. 녹는 점이 높은 미크론 크기의 입자를 추가하면 Ti-6Al-4V 합금의 2 차 상에 해당하는 1 차 결정 입자 및 변형 된 입자를 정제 할 수 있습니다. 또한 사전에 증착 된 금속 입자의 재결정 화 및 성장을 효과적으로 억제 할 수 있습니다.

Y2O3 (0, 0.12, 0.22 wt %)의 양이 다른 필러 와이어 Ti-6Al-4V 성분으로 제조 된 레이저 첨가제의 미세 구조 및 인장 특성을 조사했습니다. Y2O3의 정제 효과는 유의미했으며, Y2O3 0.22 wt %를 세로 및 가로 방향으로 포함하는 Ti-6Al-4V의 인장 강도는 Ti-6Al-4V보다 각각 약 12 ​​% 및 9 % 더 컸습니다.

동시에 어느 방향으로도 재료의 연신율에 손실이 없었습니다. 미크론 크기의 내화 입자를 사용하여 상 변환 (1 차 결정화, 고체 상 변환 및 재결정 화)을 제어하는 ​​전략은 미세 구조가 거칠어지기 쉬운 다양한 금속의 AM에 적용될 수 있습니다.

Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig1
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig1
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig2
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig2
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig3
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig3
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig4
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig4
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig5
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig5
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig6
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig6
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig7
Hierarchical grain refinement during the laser additive manufacturing of Ti-6Al-4V alloys by the addition of micron-sized refractory particles Fig7

Keywords

Grain hierarchical refinement, Yttria, Solidification microstructures, Solid phase transition microstructures, Recrystallization microstructures