Melt Pool Research Articles

Microstructure and friction properties of NiTi2-based composite layer prepared by ultrasonic assisted underwater wet laser deposition

An in situ TiC-enhanced NiTi2-based composite deposition layer was prepared by ultrasonic assisted underwater wet laser deposition. The evolution of the microstructure and interface state, and the friction properties in the air and brine solution environments of the deposition layer were analyzed and researched. The results demonstrated that the thermal and steady-state cavitation from ultrasound effects increase the total energy of the melt pool and promote mixing. The dilution rate of the ultrasonic assisted underwater laser deposition layer increases to 86.72 % compared with that of the underwater laser deposition layer (78.75 %). Ultrasonic reduced underwater laser deposition defects such as lack of fusion and weld slag, and enhanced the wettability between the deposition layer and substrate. The contact angle of the UWNT layer (24.40°, in average) is smaller than the WNT layer (29.80°, in average). Ultrasonic shortened the contact time between the deposition layer surface and the solution, which reduced the reaction of the Ni element with the brine solution. It also transformed the deposition layer from hypereutectoid microstructure to hypoeutectic microstructure and from planar interface to cellular interface. With the effect of the ultrasonic field, the elements in the deposition layer become more uniformly distributed and the secondary phases undergo spheroidization. In the ultrasonic assisted deposition layer, stress-induced FCC-Ti was discovered. Ultrasonic field also reduced the dispersion of the microhardness and increased the average microhardness to 863.3 ± 45.1 HV0.3. Tribology properties show that ultrasonic field effectively improved the wear resistance and friction stability of the ultrasonic assisted deposition layer. The COF of the ultrasonic assisted deposition layer was less affected by the environment, with values of 0.25 and 0.24 observed in air and brine solution, respectively. Overall, the research results in this paper can provide a new insight to improve the surface properties of NiTi2-based alloy underwater laser deposition.

Microstructure evolution of AlSi10Mg alloy in RAP process

Abstract With its computer-aided layer-by-layer production approach, additive manufacturing (AM) and powder bed laser fusion (PBLF) paved the way to produce metallic parts more precisely than any other manufacturing technique. However, the combinability and the interaction of this relatively new manufacturing technique with the other near-net shape production techniques is still a mystery. In this study, the recrystallization and partial melting (RAP) behavior, which is a feedstock production approach for semisolid forming methods, investigated on AlSi10Mg parts produced by PBLF and conventional casting were compared in terms of microstructural and hardness evaluations. After the reheating process, the globalization of Si particles and the breakdown of the Si network around the melt pools were displayed with light microscope and scanning electron microscope (SEM) images. The hardness values of the PBLF as-fabricated specimens were found to be significantly higher than the as-cast specimens; however, the values were almost equaled after the RAP treatment and even got lower on the bottom and top regions of the PBLF samples after 20 min of reheating because of the enlarged shrinkage porosities and the coarsened morphology.

Influence of microstructure and surface topography on material removal by the Hirtisation® process

ABSTRACT The Hirtisation® process is an electro-chemical process, wherein the electrolyte can easily access both external and internal surfaces. The process shows promising results in both support structure removal and reduction of surface roughness, and has the potential to solve the productivity and quality trade-off in powder bed fusion – laser beam (PBF-LB) processing. In this study, the role of the microstructure and surface topography on the capability of the Hirtisation® process to lower the PBF-LB produced surface roughness, has been investigated. A detailed microstructure analysis by SEM was used to determine the effect of the Hirtisation® process on removal of sintered powder, the effects on melt pool boundaries and grain boundaries, and thus the final surface quality. The Hirtisation® process significantly reduced surface roughness thanks to the complete removal of sintering powder from the as-built surface. Additionally, preferential material removal was detected along melt pool boundaries, leading to creation of notches of up to 10 µm in depth.

Machine learning analysis for melt pool geometry prediction of direct energy deposited SS316L single tracks

Machine learning analysis for melt pool geometry prediction of direct energy deposited SS316L single tracks

Process development and heat flow analysis for thin walls made of aluminum using extreme high-speed laser material deposition (EHLA3D)

Extreme high-speed laser material deposition (EHLA) is an adapted variant of directed energy deposition (DED-LB-P/M), also known as laser material deposition, and has been developed for the efficient manufacturing of thin layers with high deposition speeds. With precise control of the energy input into the powder gas jet and the substrate, EHLA allows deposition speeds of up to 200 m/min and weld beads as thin as 25 μm. Advantages include a smaller melt pool and a heat-affected zone, allowing the processing of difficult-to-weld material combinations. The development of EHLA for additive manufacturing (EHLA3D) aims to produce highly customized components with improved structural accuracy compared to standard LMD at increased build rates compared to laser powder bed fusion (PBF-LB/M). A promising application is complex lightweight structures for the aerospace industry. However, there is a lack of systematic investigation on lightweight materials processed with EHLA3D at feed rates >20 m/min. In this work, a specially designed tripod machine (maximum feed rate 200 m/min) was used to investigate the buildup of aluminum in process regimes at 30 m/min. After confirming the existing single-track parameters, the tracks were metallographically examined and checked for pores, cracks, and bonding defects. The process was applied to thin-wall geometries and line energies as well as return-times that were varied. To gain an understanding of process-induced heat development, the process was monitored using thermography. Since the process shows geometry-specific heat flow patterns, guidelines have been developed that enable the buildup using different process adaptions.

Investigation on metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow

High-power laser welding processes involve intense interactions between the laser beam and the base material, resulting in severe welding defects such as humping, spattering, and undercutting. Utilizing side gas flow may provide an effective approach for minimizing these defects. However, the effects of side gas flow on the dynamic behavior and weld formation necessitate further investigation. In this study, an innovative analysis of metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow is presented, combining experimental and simulation results. A three-dimensional transient fluid flow model was developed, uniquely integrating an adaptive heat source, evaporation-condensation processes, and metal vapor energy attenuation to provide a novel perspective on the effects of side gas flow in high-power laser welding. The results display that side gas flow could suppress plasma, increase thermal input to the melt pool, and intensify the flow of liquid metal toward the pool bottom during high power laser welding, thereby enhancing weld seam penetration. The numerical results indicate that variations in flow rate significantly impact metal vapor morphology, with higher flow rates reducing both the average area and height of the metal vapor and effectively suppressing the size of metal vapor/plasma. When the side gas flow rate is 20 l/min, with the gas flow impact point located at the keyhole opening and the nozzle height set to 3 mm, the side gas flow significantly enhances the depth-to-width ratio of the weld seam in 316L stainless steel laser welding. This work can provide guidance for suppression of weld defects in high-power laser welding of medium-thick steel components, which has important theoretical significance and application value.

Boosting Coercivity of 3D Printed Hard Magnets through Nano-Modification of the Powder Feedstock.

The demand for strong, compact permanent magnets essential for the energy transition drives innovation in magnet manufacturing. Additive manufacturing, particularly Powder Bed Fusion of metals using a laser beam (PBF-LB/M), offers potential for near-net-shaped Nd-Fe-B permanent magnets but often falls short compared to conventional methods. A less explored strategy to enhance these magnets is feedstock modification with nanoparticles. It is demonstrated that modifying a Nd-Fe-B-based feedstock with 1wt.%Ag nanoparticles boost the coercivity of the magnets to a record value of 935±6kAm-1 without further post-processing or heat treatments. Suitable volumetric energy densities for the PBF-LB/M process are determined using finite element simulations predicting melt pool behavior and part density. Microstructural analyses reveal finer grain sizes and more equiaxed nanocrystalline structures due to the modification. Atom probe tomography identifies three phases in the Ag-modified samples, with Ag forming nanophase regions with rare-earth elements near the amorphous Zr-Ti-B-rich intergranular phase, potentially decoupling the Nd2Fe14B primary phase. The study shows that superior magnetic properties primarily result from microstructure modification rather than part density. These findings highlight inventive material design approaches via feedstock surface modification to achieve superior magnetic performance in additively manufactured Nd-Fe-B magnets.

A multiscale model for efficiently simulating laser powder bed fusion process with detailed microstructure and mechanical performance results

Numerical simulation is regarded as an important method for studying the mechanisms of additive manufacturing (AM), especially in building a multiscale simulation model. However, the conversion of physical phenomena and parameters across scales is complex, and the number of simulation elements often changes extremely, leading to an inherent conflict between simulation accuracy and efficiency. Therefore, this work introduces a model that balances the need for detailed grain morphology and overall simulation efficiency, to investigate the relationship between process parameters, microstructure, and mechanical performance during Inconel 718 laser powder bed fusion (L-PBF) process. The cellular automata - finite element method (CA-FEM) was used to simulate the melt pool forming and predict the microstructure evolution. Based on the CA result, the tensile process was simulated through crystal plasticity-finite element method (CP-FEM). Specially, the CA-FEM model was simplified and sliced layer-by-layer to reduce simulation time and data storage, supporting parallel computation. The prediction time for the microstructure growth of millions of elements was less than 1.5 h. The CP-FEM model was simplified by reasonably reducing elements in the representative volume element (RVE) model, improving the simulation efficiency by 73 %. The simulation results were validated through EBSD observation and tensile tests, showing good agreement with experimental results, with the final simulation error for mechanical performance not exceeding 10 %. The effects of process parameters on microstructure and mechanical performance were comprehensively discussed. This model supports the optimization of L-PBF process parameters for Ni-based alloys and provides a reference for improving the efficiency of multiscale simulations for other AM processes and materials.

Additive manufacturing between cooled confinements with the LDNA process

Laser-assisted double-wire welding with nontransferred arc (LDNA) is characterized by two converging wires between which an electrical arc burns to melt both wires. The molten material falling onto the substrate is distributed with oscillating laser radiation with a power of 1.5 kW to ensure sufficient bonding with the substrate without delamination and pores. The process is characterized by high deposition rates of more than 7.5 kg/h. Due to the high deposition rate, only high values for waviness in the buildup direction can be achieved in the production of multilayer additive structures. The approach investigated in this publication examines the potential to produce additive structures with a confined melt pool. The use of water-cooled copper jaws and the deposition of ER70S-6 between these confinements using the LDNA process are being investigated to produce additive 10 mm wide and 100 mm long structures with significantly improved waviness in the direction of buildup and improved dimensional accuracy. It can be shown that a wall-like structure can be welded between the confinements without material bonding to the cooling jaws. Additionally, it has been observed that the confinements can easily be removed which is attributed to the thermal contraction of the steel. Metallographic examinations of the produced structures in the longitudinal and transverse sections as well as hardness curves in the transverse section are carried out and evaluated. Multilayer structures with up to five layers are produced and the waviness and surface roughness on the side surfaces defined by the jaws are measured and evaluated.

Thermodynamic behavior and microstructure evolution of Inconel 718 alloy by laser metal deposition

The temperature evolution, stress evolution, and dendrite growth during the laser metal deposition (LMD) process of Inconel 718 alloy were simulated using a multi-scale model that combines the finite element method and the Cellular Automata (CA) method. This model established the relationship between the thermal behavior of the molten pool and the solidification characteristics, and predicted the morphological size of the solidified structure. Research indicates that under conditions of higher cooling rate and lower shape control factor, equiaxed grains are prone to form, with a lower degree of elemental segregation in this region, which is conducive to the precipitation of granular Laves phase. Conversely, under conditions of lower cooling rate and higher shape control factor, columnar grains are more likely to form, with a higher degree of elemental segregation in this region, leading to the precipitation of chain-like Laves phase. The results of thermo-mechanical coupled simulation suggest that the maximum transient thermal stress is located at the overlap position, and when the component cools down to room temperature, the maximum normal stress along the scanning direction is observed. Dendritic growth results demonstrate that during the equiaxed grain growth process in the top region of the melt pool, the released solute is constrained by time and space, leading to the accumulation of solute and the formation of interdendritic segregation. In areas with a higher grain density, the solute accumulation zones overlap, resulting in an increase in solute concentration, which inhibits dendrite growth. In the middle region of the melt pool, during the columnar grain growth process, the solute concentration in the gaps between adjacent grains continuously increases, resulting in micro-segregation phenomena. Experimental measurements have shown that the temperature field's melt pool morphology, stress values along the scanning path, and dendritic morphology are in good agreement with the experimental outcomes.

Evolutionary Mechanism of Solidification Behavior in the Melt Pool during Disk Laser Cladding with 316L Alloy

Laser cladding is an emerging environmentally friendly surface-strengthening technology. During the cladding process, the changes in molten pool temperature and velocity directly affect the solidification process and element distribution. The quantitative revelation of the directional solidification mechanism in the molten pool during the cladding process is crucial for enhancing the quality of the cladding layer. In this study, a multi-field coupling numerical model was developed to simulate the coating process of 316L powder on 45 steel matrices using a disk laser. The instantaneous evolution law of the temperature and flow fields was derived, providing input conditions for simulating microstructure evolution in the molten pool’s paste zone. The behavior characteristics of the molten pool were predicted through numerical simulation, and the microstructure evolution was simulated using the phase field method. The phase field model reveals that dendrite formation in the molten pool follows a sequence of plane crystal growth, cell crystal growth, and columnar crystal growth. The dendrites can undergo splitting to form algal structures under conditions of higher cooling rates and lower temperature gradients. The scanning speed of laser cladding (6 mm/s) has minimal impact on dendrite growth; instead, convection within the molten pool primarily influences dendrite growth and tilt and solute distribution.

Vacuum laser zone refining of titanium towards lunar metallurgy: Experimental and numerical study

The development of in-situ utilisation technologies for lunar resources is crucial for future human deep-space exploration. This paper presents a novel vacuum laser zone refining technique aimed at in-situ separation of titanium and iron. The experimental and numerical simulation results indicate that increasing laser power while reducing the melting speed significantly increases the temperature gradient of the melt pool, thereby enhancing molten flow velocity. These factors effectively redistribute the elements at the solid-liquid interface, improving Fe and Ti separation efficiency. Additionally, increasing the number of refining passes can also significantly improve the separation efficiency of Fe and Ti. Under the conditions of 1000 W laser power, 0.05 mm/s melting speed, and 5 refining passes, the separation efficiency of Fe reached 76.5 %. Notably, the maximum molten flow velocity reached 0.157 m/s, which ensured a uniform distribution of Fe in the melting zone. Hence, the proposed vacuum laser zone refining technique is a promising approach for efficient separation of titanium and iron from titanium–iron alloys, providing potential support for deep-space exploration efforts.

Classification of melt pool states for defect detection in laser directed energy deposition using FixConvNeXt model

Abstract Laser directed energy deposition (L-DED) has emerged as a promising technique for rapid prototyping due to its cost-effectiveness and efficiency. However, the intricate and multi-scale physics of the process hinder its widespread application. This paper addresses the challenge by focusing on real-time identification of melt pool states to detect defects early and minimize resource wastage. To achieve this, a FixConvNeXt model was developed for fast and accurate monitoring of melt pool states. This model was trained using 5000 melt pool images captured during the printing of single-track deposits from a charge-coupled device. To evaluate its performance, FixConvNeXt was compared with other models using various metrics. Experimental results demonstrated that FixConvNeXt achieved superior performance in accurately identifying melt pool states with 99.1% accuracy, while also reducing computation burden and processing time. The mechanism of classification by FixConvNeXt was explained using gradient-weighted class activation mapping. The research findings highlight the potential application of online process monitoring in L-DED. This study lays the foundation for future development of an efficient deep learning network for automatic defect detection and feedback control.

Thermal experiment study on the self-luminous properties of metallic iron during solid–liquid phase transition

According to the thermal experiment study of the self-luminescence spectrum of industrially pure iron (DT8) at a heating and cooling rate of 5 °C/min, at the moment of 0 (800 °C), DT8 had no significant self-luminescence characteristics in the wavelength range of 200–1100 nm. At the same time, the first-order differentiation of the spectral intensity versus time was equal to zero at the beginning and end moments of the solid-liquid phase transition. When the solid-liquid melt temperatures are equal (i.e. 1531 °C), there are two sharp peaks at wavelengths of 589.1 nm and 766.7 nm of the self-luminous spectrum in the pure liquid state compared to the self-luminous spectrum in the pure solid state. The intensity of the spectrum decreases significantly as the metallic iron changes from the pure solid phase to the pure liquid phase, with a reduction rate greater than 20%. The appearance of the fitted peaks at 589.1 nm and 769 nm was found by XPS fitting analysis to be a significant feature of the difference in the auto-luminescence spectra of pure solid phase and pure liquid phase metallic iron at a constant melt pool temperature. After the transformation of pure solid phase into pure liquid phase, the decay rate of the self-luminous spectrum in the long-wave direction at wavelengths greater than 762 nm is greater than that in the short-wave direction at wavelengths less than 625 nm.

Investigation of surface structuring and oxidation performance of Inconel 718 superalloy by laser remelting with different patterns

The current paper deals with the effect of CO2 laser remelting on the surface structuring and oxidation performance of Inconel 718 superalloy, pointing out different laser-induced surface patterns that make a difference in their oxidation properties vital for high-temperature applications. Surface roughness, microstructure, and oxidation behavior characterization were performed using 3D optical profilometry, SEM, and XRD techniques. The oxidation tests conducted at 1000 °C for 24 h have revealed that remelted surfaces offered better oxidation resistance compared to untreated samples. Notably, the patterned sample showed the lowest weight gain under oxidation, and a parabolic regime in oxidation occurred after 100 min; while in an untreated reference sample, this appears only after 200 min. This improvement in performance results from the formation of a chromium-rich oxide layer on the melt pools, which acts as an effective barrier against further oxidation. The findings show that laser remelting, especially with grid-like surface patterns, results in an improvement in both durability and high-temperature performance of Inconel 718; therefore, it is apparently a very promising technique for lifespan extension of industrially relevant materials.

Temperature measurement in laser–metal processing using optical sensing: Radiometric calibration and validation of a multispectral camera

In laser–metal processing such as Laser-based Powder Bed Fusion of Metals (PBF-LB/M), the quality of the final product is significantly influenced by the thermal behaviour of the melt pool. Accurate temperature measurements are challenging due to high temperature gradients and rapid cooling. This study introduces Multispectral Imaging (MSI) as a highly effective thermometry technique to address these demanding conditions. MSI captures multiple bands of radiation, enabling the simultaneous determination of absolute temperature and surface emissivity. This capability is crucial for ensuring high-quality outcomes in laser–metal processing such as PBF-LB/M, contingent upon robust radiometric calibration.To enhance reliability, two radiometric calibration models were developed: an empirical model based on linear sensor data correlations and an analytical model leveraging sensor behaviour. An efficient calibration was found for both models across a range of signal-to-noise ratios in the black body calibrator, where the analytical model even performs robust under a high noise level.Additionally, the temperature accuracy in the solid-state case was tested with a thermo-mechanical simulator. Results showed that the empirical and analytical models achieved mean relative errors of 2.0% and 1.6%, respectively, outperforming the state-of-the-art. Further, laser irradiation experiments highlighted the analytical model’s ability to accurately determine the emissivity decrease during the solid-to-liquid transition, allowing for accurate melt pool temperature estimations. Conversely, the empirical model struggled to estimate temperature effectively in the liquid phase.This study not only proposed a robust methodology of MSI in temperature measurement but also confirmed the accuracy and reliability of the system, broadening the scope for further investigation into the intricate thermal dynamics involved in laser–metal interactions.

Research on energy utilization of electron beam melting for silicon purification

As a key material for solar photovoltaic power generation, the purity of silicon plays a crucial role in the photovoltaic conversion efficiency and performance. The electron beam melting (EBM), which is irreplaceable metallurgical methods, has been widely used for silicon purification. However, high energy consumption result in relatively high cost, which limits its widespread application in melting industry. This study was centered on the energy distribution that proposes a new approach to reducing energy consumption during EBM. The scanning form of electron beam is most important factor concerning energy consumption. Different scanning forms can affect the characteristics of molten pool which is closely correlated with the purification process. In this study, efficient and energy-saving preparation processes of EBM are being explored through the numerical model and experimental. The relationship of energy distribution form and purification efficiency is studied. The research results indicate that electron beam scanning under uniform distribution can achieve more uniform temperature and flow field distribution in the molten pool, which has a higher energy utilization rate during silicon purification by EBM. The mathematical model established in this study can effectively predict the energy consumption level under different melting parameters, providing important reference for the optimization and energy conservation of EBM process for other materials. In addition, evaporation characteristics of volatile impurity, migration of the second phase particles in the melt, controlling of melt pool characteristics and the crystal growth control all can be conducted based on this study.

The effects of specimens geometry on solidification conditions and microstructure formation in laser powder bed fusion fabricated Ti–6Al–4V alloys

Laser powder bed fusion (LPBF) excels at creating intricately shaped parts, which will result in variations in solidification conditions, microstructure formation and mechanical properties. To address this issue, three distinct shapes: cubic, pyramidal and inversed pyramidal Ti–6Al–4V alloy specimens were fabricated using LPBF technology. The effects of specimen geometry on microstructure formation, transformation as well as its effects on mechanical properties were investigated in the present study. Our results show that specimen geometry significantly affects the thermal gradient, influencing nucleation and growth during fabrication. EBSD (Electron Backscatter Diffraction) characterization reveals that the primary β-phase grows in columnar grains in cubic specimens, coarse columnar grains along lateral faces in pyramidal specimens, and nearly equiaxed grains in inverted pyramidal specimens, leading to a significant reduction in texture. Nanoindentation tests show higher nanohardness in the top parts of cubic and pyramidal specimens compared to the bottom parts, while inverted pyramidal specimens have consistent nanohardness throughout. This variation is due to differences in solid solute concentration, melt pool undercooling, and thermal histories during and post solidification processes respectively. TEM results indicate that the fine lath phase on the top parts has transformed into β-phase, while the bottom parts remain as α′ phase, highlighting a disparity due to different thermal cycling times and temperatures.

Gap tolerance and molten pool destabilization mechanism in oscillating laser-arc hybrid welding of aluminum alloys

Oscillating laser-arc hybrid welding (O-LAHW) offers significant advantages in enhancing efficiency and mechanical properties. However, in actual production, gap fluctuations can cause instability, limiting its application in large-scale structure manufacturing. In this study, we explored the impact of gap fluctuation on the destabilization of the molten pool in aluminum alloy O-LAHW and identified the maximum gap tolerance for various conditions. High-speed photography revealed that the oscillating molten pool undergoes a transitional state of periodic collapse before complete instability, a behavior distinct from that of a non-oscillating molten pool. We also analyzed the variations in weld geometry prior to destabilization and developed a global force model of the molten pool to identify key geometrical parameters and related driving forces contributing to destabilization. The results show that maintaining a surface tension ratio of over 55 % at the root of the molten pool is crucial for its stability. Additionally, the effects of oscillatory behavior and gap variations on the laser-substrate interaction were explored, revealing the physical mechanisms behind the changes in key geometrical parameters of the melt pool cross-section. The centrifugal effect generated by high-frequency oscillation is identified as a crucial mechanism for extending the duration of periodic collapse compared to non-oscillating molten pools. By discussing the interactions between energy absorption, molten pool shape, and molten pool forces, the study reveals the evolution process of weld destabilization and explains the differences in gap tolerance between oscillating and non-oscillating laser-arc hybrid welding, providing a reference for improving weld stability.

Alkali-carbonate melts in the cratonic mantle evidenced by a wehrlite xenolith from the Majuagaa kimberlite, West Greenland

Carbonate melts are critically important for the deep carbon cycle, mantle melting, redox reactions, and transport of highly incompatible elements. The presence of carbonate melts in the cratonic mantle has been inferred from experimental studies, metasomatic transformations, and melt/fluid inclusions in xenoliths, kimberlites, and diamonds. However, the exact composition of such melts is difficult to determine due to their ephemeral nature and highly reactive properties. Once formed, they migrate away from the source and react with silicate mantle minerals, especially orthopyroxene, causing mantle metasomatism. Wehrlite is one of the products of interaction between the carbonate melt and peridotitic mantle and hence is an excellent candidate for locating in situ carbonate melts. Here, we report petrological, geochemical, and melt inclusion data for a garnet wehrlite xenolith in the Majuagaa kimberlite dike, West Greenland. The xenolith, which last equilibrated with the mantle at 4.5 GPa and 1000 °C, contains abundant melt pools composed of dolomite, calcite, serpentine, spinel, apatite, and phlogopite. Although the original magmatic mineralogy was largely destroyed by low-temperature alteration, remnants of the crystallized carbonatitic melt are preserved as primary melt inclusions in the liquidus Ti-Mg-Fe spinel. These melt inclusions, composed of carbonates, alkali carbonates, periclase/brucite, and minor halides, K-sulfide, apatite, and phlogopite, are the first direct evidence for in situ alkali-carbonate melt in the deep cratonic mantle. Compositionally, they are very similar to primary Na-dolomite melt found in experiments and in fluid inclusions within diamonds.