TiMoZrTaSi alloys appertain to a new generation of metallic biomaterials, labeled high-entropy alloys, that assure both biocompatibility as well as improved mechanical properties required by further medical applications. This paper presents the use of nondestructive evaluation techniques for new type of alloys, TiMo₂₀Zr₇Ta₁₅Si_x, with x = 0; 0.5; 0.75; 1.0, which were obtained by vacuum melting. In Ti alloys, the addition of Mo improves tensile creep strength, Si improves both the creep and oxidation properties, Zr leads to an α crystalline structure, which increases the mechanical strength and assures a good electrochemical behavior, and Ta is a β stabilizer sustaining the formation of solid β-phases and contributes to tensile strength improvement and Young modulus decreasing. The effects of Si content on the mechanical properties of the studied alloys and the effect of the addition of Ta and Zr under the presence of Si on the evolution of crystallographic structure was studied. The influence of composition on fracture behavior and strength was evaluated using X-ray diffraction, resonant ultrasound spectroscopy (RUS) analyses, SEM with energy dispersive X-ray spectroscopy, and acoustic emission (AE) within compression tests. The β-type TiMo₂₀Zr₇Ta₁₅Si_x alloys had a good compression strength of over 800 MPa, lower Young modulus (69.11–89.03 GPa) and shear modulus (24.70–31.87 GPa), all offering advantages for use in medical applications.

Current metal additive manufacturing (AM) technologies imply complicated processes, with many variable parameters determining their performance and the quality of the resulting product. Process optimisation requires feedback from nondestructive evaluation (NDE) of the additively manufactured parts. The presence of a complicated internal structure and complex shapes and geometries are limiting factors in the application of standard, preferably online, NDE techniques for quantitative assessment of process-related defects such as irregular internal structure, porosity, etc. In this study, potential non-linear elastic wave spectroscopy (NEWS) methods were tested to classify two types of artificially created defect in Ti-6Al-4V prismatic samples fabricated by an electron beam melting (EBM) system. Two series of samples with variable internal defects were tested: samples with central circular defects (missing material gaps) and samples with gradually growing stochastic porosity. Each group of samples also contained a fully compact sample for comparison. Additional ultrasonic NEWS procedures were then tested to classify the variability of defects. A relatively simple experimental facility with two piezoelectric transducers allowed samples to be analysed and the results recorded. The best results, documented in this paper, were obtained using two modifications of the non-linear wave modulation spectroscopy (NWMS) procedure. One group was successfully classified with two mixed excitation frequencies; slopes of amplitude-dependent inter-modulation sidebands identified samples with growing defect thickness. For the second group, longer chirp excitation was used mixed with signals of constant frequency and/or without any mixing. Growing dispersed stochastic porosity was successfully classified using these methods. The results of NEWS tests indicate that selected NEWS procedures can also be used for online AM monitoring.

The method of making parts through additive manufacturing (AM) is becoming more and more widespread due to the possibility of the direct manufacturing of components with complex geometries. However, the technology’s capacity is limited by the appearance of micro-cracks/discontinuities during the layer-by-layer thermal process. The ultrasonic (US) method is often applied to detect and estimate the location and size of discontinuities in the metallic parts obtained by AM as well as to identify local deterioration in structures. The Ti6Al4V (Ti64) alloy prepared by AM needed to acquire a high-quality densification if remarkable mechanical properties were to be pursued. Ultrasonic instruments employ a different type of scanning for the studied samples, resulting in extremely detailed images comparable to X-rays. Automated non-destructive testing with special algorithms is widely used in the industry today. In general, this means that there is a trend towards automation and data sharing in various technological and production sectors, including the use of intelligent systems at the initial stage of production that can exclude defective construction materials, prevent the spread of defective products, and identify the causes of certain instances of damage. Placing the non-destructive testing on a completely new basis will create the possibility for a broader analysis of the primary data and thus will contribute to the improvement of both inspection reliability and consistency of the results. The paper aims to present the C-scan method, using ultrasonic images in amplitude or time-of-flight to emphasize discontinuities of Ti64 samples realized by laser powder-bed fusion (L-PBF) technology. The analysis of US maps offers the possibility of information correlation, mainly as to flaws in certain areas, as well as distribution of a specific flaw in the volume of the sample (flaws and pores). Final users can import C-scan results as ASCII files for further processing and comparison with other methods of analysis (e.g., non-linear elastic wave spectroscopy (NEWS), multi-frequency eddy current, and computer tomography), leading to specific results. The precision of the flight time measurement ensures the possibility of estimating the types of discontinuities, including volumetric ones, offering immediate results of the inspection. In situ monitoring allows the detection, characterization, and prediction of defects, which is suitable for robotics. Detailing the level of discontinuities at a certain location is extremely valuable for making maintenance and management decisions.

In this letter, fundamentals of transferring a time reversal experiment between similar objects are discussed. The time reversal experiment consists of two steps: forward propagation, when a source excites the medium and a complex wave field is created, and back propagation, resulting in time reversal focusing. Here the procedure of performing the first step on one specimen and the second step on another is investigated. The theory of time reversal transfer is explained on an example of object shape variations. However, conclusions of the theoretical analysis are applicable universally. The feasibility of the proposed procedure is validated in experiments modeling conditions in practice.

Time reversal (TR) ultrasonic signal processing is now broadly used in a variety of applications, and also in NDE/NDT field. TR processing is used e.g. for S/N ratio enhancement, reciprocal transducer calibration, location, identification, and reconstruction of unknown sources, etc. TR procedure in con-junction with nonlinear elastic wave spectroscopy NEWS is also useful for sensitive detection of defects (nonlinearity presence). To enlarge possibilities of acoustic emission (AE) method, we proposed the use of TR signal reconstruction ability for detected AE signals transfer from a structure with AE source onto a similar remote model of the structure (real or numerical), which allows easier source analysis under laboratory conditions. Though the TR signal reconstruction is robust regarding the system variations, some small differences and changes influence space-time TR focus and reconstruction quality. Experiments were performed on metallic parts of both simple and complicated geometry to examine effects of small changes of temperature or configuration (body shape, dimensions, transducers placement, etc.) on TR reconstruction quality. Results of experiments are discussed in this paper. Considering mathematical similarity between TR and Coda Wave Interferometry (CWI), prediction of signal reconstruction quality was possible using only the direct propagation. The results show how some factors like temperature or stress changes may deteriorate the TR reconstruction quality. It is also shown that sometimes the reconstruction quality is not enhanced using longer TR signal (S/N ratio may decrease).