Critical crystallization properties of an industrial-grade Zr-based metallic glass used in additive manufacturing

Sohrabi, Navid; Schawe, J.E.K.; Jhabvala, Jamasp; Löffler, Jörg F.; Logé, Roland E.

doi:10.1016/j.scriptamat.2021.113861

Cited by 30 publications

(29 citation statements)

References 40 publications

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“…We recently studied crystallization of AMZ4 [67] and showed that the time to crystallization is in the order of 3 ms in the 750-800 • C temperature range, which effectively prevents the fabrication of fully amorphous AM parts. Bordeenithikasem et al [9] showed that crystallization of AMZ4 results in an increase of hardness and brittleness, making the material prone to cracking, which is consistent with the results of reference [60].…”

Section: Discussionmentioning

confidence: 99%

“…Although the strategy of increasing the laser power in the near-surface region slightly increased the crystallized fraction, it was effective in reducing the LoF content, thereby significantly increasing the tensile strength (by 27%) [40]. Reducing porosity content by hot isostatic pressure (HIP) post-treatment, as done for crystalline alloys [69], is not an option for BMGs, due to the associated extensive crystallization, especially for AMZ4 exhibiting high critical heating and cooling rates [67].…”

Section: Discussionmentioning

confidence: 99%

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Fatigue Performance of an Additively Manufactured Zr-Based Bulk Metallic Glass and the Effect of Post-Processing

Sohrabi

Nasab

Rouxel

et al. 2021

Metals

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Fatigue is the most common cause of failure of mechanical parts in engineering applications. In the current work, we investigate the fatigue life of a bulk metallic (BMG) glass fabricated via additive manufacturing. Specimens fabricated via laser powder-bed fusion (LPBF) are shown to have a fatigue ratio of 0.20 (fatigue limit of 175 MPa) in a three-point bending fatigue test. Three strategies for improving the fatigue behavior were tested, namely (1) relaxation heat treatment, giving a slight fatigue life improvement at high loading conditions (≥250 MPa), (2) laser shock peening, and (3) changing the build orientation, the latter two of which yielded no significant effects. It was found that the presence of lack of fusion (LoF) had the preponderant effect on fatigue resistance of the specimens manufactured. LoF was observed to be a source of stress localization and initiation of cracks. The fatigue life in BMGs fabricated by LPBF is thus primarily influenced by powder quality and process-induced defects, which cannot be removed by the post-treatments carried out in this study. It is believed that a slight increase in laser power, either in the near-surface regions or in the core of the specimens, could improve the fatigue behavior despite the associated (detrimental) increase of crystallized fraction.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Fatigue Performance of an Additively Manufactured Zr-Based Bulk Metallic Glass and the Effect of Post-Processing

Sohrabi

Nasab

Rouxel

et al. 2021

Metals

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“…Although XRD could not detect crystallization for Set A, the increased crystallized fraction measured by DSC from Sets A to C is in agreement with the XRD results. In our previous work [ 47 ], using fast scanning calorimetry, we showed that the thermal stability of AMZ4 is low and that the time to crystallization at the nose of the time-temperature-transformation (TTT) diagram is less than 4 ms, which is sufficient for the formation of nanocrystals during the LPBF process.…”

Section: Discussionmentioning

confidence: 99%

Tensile and Impact Toughness Properties of a Zr-Based Bulk Metallic Glass Fabricated via Laser Powder-Bed Fusion

et al. 2021

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In the past few years, laser powder-bed fusion (LPBF) of bulk metallic glasses (BMGs) has gained significant interest because of the high heating and cooling rates inherent to the process, providing the means to bypass the crystallization threshold. In this study, (for the first time) the tensile and Charpy impact toughness properties of a Zr-based BMG fabricated via LPBF were investigated. The presence of defects and lack of fusion (LoF) in the near-surface region of the samples resulted in low properties. Increasing the laser power at the borders mitigated LoF formation in the near-surface region, leading to an almost 27% increase in tensile yield strength and impact toughness. Comparatively, increasing the core laser power did not have a significant influence. It was therefore confirmed that, for BMGs like for crystalline alloys, near-surface LoFs are more detrimental than core LoFs. Although increasing the border and core laser power resulted in a higher crystallized fraction, detrimental to the mechanical properties, reducing the formation of LoF defects (confirmed using micro-computed tomography, Micro-CT) was comparatively more important.

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“…Using fast differential scanning calorimetry (FDSC), the TTT diagram of AMZ4 with a high oxygen content (1200-1400 ppm) was measured. The time to crystallization was on the order of 3 ms in the 750-800 • C temperature range, which effectively prevents the fabrication of fully amorphous AM parts [154]. Several studies on the LPBF of AMZ4 [32,55,56] attributed the present nanocrystals to Cu 2 Zr 4 O phase.…”

Section: Change In the Chemical Compositionmentioning

confidence: 99%

“…They used the heating rate of 20 K/s to measure T x with a conventional DSC system. However, higher heating rates shift T x to higher temperatures [154]. Sohrabi et al [32] used FDSC to measure T x of AMZ4 powder at the heating rate of 10 4 K/s and used it as a criterion to predict the region more sensitive to crystallization.…”

Section: Time Spent At Temperatures Higher Than T Xmentioning

confidence: 99%

Additive Manufacturing of Bulk Metallic Glasses—Process, Challenges and Properties: A Review

Sohrabi

Jhabvala

Logé

2021

Metals

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Bulk Metallic Glasses (BMG) are metallic alloys that have the ability to solidify in an amorphous state. BMGs show enhanced properties, for instance, high hardness, strength, and excellent corrosion and wear resistance. BMGs produced by conventional methods are limited in size due to the high cooling rates required to avoid crystallization and the associated detrimental mechanical properties. Additive manufacturing (AM) techniques are a potential solution to this problem as the interaction between the heat source, e.g., laser, and the feedstock, e.g., powder, is short and confined to a small volume. However, producing amorphous parts with AM techniques with mechanical properties comparable to as-cast samples remains a challenge for most BMGs, and a complete understanding of the crystallization mechanisms is missing. This review paper tries to cover recent progress in this field and develop a thorough understanding of the correlation between different aspects of the topic. The following subjects are addressed: (i) AM techniques used for the fabrication of BMGs, (ii) particular BMGs used in AM, (iii) specific challenges in AM of BMGs such as the control of defects and crystallization, (iv) process optimization of mechanical properties, and (v) future trends.

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Critical crystallization properties of an industrial-grade Zr-based metallic glass used in additive manufacturing

Cited by 30 publications

References 40 publications

Fatigue Performance of an Additively Manufactured Zr-Based Bulk Metallic Glass and the Effect of Post-Processing

Fatigue Performance of an Additively Manufactured Zr-Based Bulk Metallic Glass and the Effect of Post-Processing

Tensile and Impact Toughness Properties of a Zr-Based Bulk Metallic Glass Fabricated via Laser Powder-Bed Fusion

Additive Manufacturing of Bulk Metallic Glasses—Process, Challenges and Properties: A Review

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