Data and Programs Data of project "Research and Development of Ta-Ti-V-W High-Entropy Alloys for Generation IV Fusion Reactors" is being prepared for future publication. The dataset includes: Scanning Electron Microscopy (SEM) images, readable using standard image processing software. Differential Scanning Calorimetry (DSC) raw data, compatible with standard graphing software. Microhardness and nanohardness data spreadsheets, which can be opened using conventional spreadsheet software. SEM/EDS raw data, including compositional maps and point analyses. These provide detailed compositional data for the as-cast, homogenised, and annealed samples, and can be opened using the Oxford Instruments AZtec software. X-ray Diffraction (XRD) raw data, accessible via conventional spreadsheet or XRD data processing software. Methodology The alloy compositions studied — Ta25Ti35V25W15, Ta25Ti30V25W20, Ta25Ti25V25W25, and Ta25Ti20V25W30 — were developed as part of a project aimed at designing a new class of metallic materials for potential use in future fusion energy systems, a field regarded as essential for achieving clean and sustainable energy. The objective was to create alloys that meet the environmental and safety criteria defined by UK nuclear materials regulations, particularly concerning long-term radioactivity and structural stability. Alloys were produced by arc melting pure elements (≥99.9% purity). Each ingot was inverted and remelted at least five times to minimise compositional inhomogeneity. All alloys were homogenised at 1600 °C for 24 hours using a vacuum furnace equipped with a graphite heating element. Subsequently, samples were annealed at 700 °C, 900 °C, and 1100 °C for 1000 hours and quenched in cold water. Annealing was performed in argon-backfilled quartz ampoules to minimise environmental contamination. DSC was performed on disc-shaped specimens (5 mm diameter × 1 mm thickness) cut from as-cast ingots. SEM specimens were prepared using standard metallographic techniques, finishing with a final polish in a 0.06 μm colloidal silica solution neutralised with H₂O₂. SEM/EDS analysis was conducted using a Zeiss GeminiSEM 300, equipped with an Oxford Instruments EDX detector. Actual alloy compositions were determined from the homogenised state by averaging results from at least five large, randomly selected areas per sample. Compression tests were carried out using an Instron 8501 universal testing machine (100 kN capacity). Microhardness measurements were performed using a Qness Q10A+ microhardness tester (ATM), while nanohardness was assessed using a KLA iNano nanoindenter. X-ray diffraction (XRD) analysis was performed using two instruments: Bruker D8 Advance (B3) with Cu Kα₁,₂ radiation, operated in rotating sample mode. Bruker D8 Advance (B1) with Co Kα₁,₂ radiation, used primarily for clean, unmounted samples in rotating mode.In addition, some specimens were mounted in ConductoMount (a conductive mounting compound by MetPrep) for subsequent SEM and EDS analysis. For these mounted samples, XRD spectra were acquired in static mode (no rotation).